Edge care routine for fine textured hair: the complete guide
Last updated 2026-07-09
TL;DR
Fine textured strands have a smaller diameter, so edges snap and thin faster than coarse hair and become vulnerable to traction alopecia. A good edge care routine for fine hair keeps tension low, moisture first, and the scalp stimulated. Most people see visible regrowth in 3 to 6 months once they stop the damage and stay consistent.
Why are fine textured hair edges so fragile compared to other hair types?
Fine hair and fine textured hair are two different things, and confusing them sends you toward the wrong routine. Texture (type 3 and type 4 curl patterns) describes the curl shape. Strand diameter is the fine-versus-coarse spectrum. You can have coarse, thick 4C strands or fine, thin 4A strands. Plenty of Black women and women with textured hair have strands that are both tightly coiled and fine in diameter. That's a double vulnerability.
A fine strand has a smaller cortex, less structural protein per inch, and a thinner cuticle layer. Under a microscope, the cuticle cells of fine hair overlap less, which means less natural protection against friction, tension, and moisture loss [1]. The edges (the hairline across the forehead, temples, and nape) carry extra anatomical disadvantages: those follicles already produce shorter, finer terminal hairs than the follicles on top of your scalp, and the skin there is thinner.
Layer tight styling on top of fine-diameter strands in an already-weak spot and the margin for error disappears fast. The American Academy of Dermatology says repeated tension on hair follicles causes traction alopecia, which begins as reversible inflammation and progresses to permanent follicle scarring if the tension keeps up [2]. Fine hair reaches that point faster than coarse hair because each strand withstands less force before the follicle is affected.
Here's the practical read: whatever tension, heat, and product load your edges can tolerate, it's probably less than you think if your strands are fine.
What does traction alopecia look like on fine textured edges?
Traction alopecia on fine textured hair starts quietly. The early signs are easy to miss, or easy to write off as seasonal shedding or stress.
Early signs include a widening or recession at the temples, small broken hairs (not shed hairs with roots attached, but snapped mid-shaft stubs) along the hairline, itching or tenderness after a style goes in, and redness or small follicle bumps called follicular pustules [2]. On fine textured hair, the hairline often looks like it's thinning rather than receding in a sharp line, because losing individual fine strands doesn't leave an obvious gap right away.
Later-stage traction alopecia shows up as smooth, shiny skin at the hairline where follicles have been destroyed and replaced by scar tissue. At that point hair does not regrow, even with treatment [3]. A 2016 study in the Journal of the American Academy of Dermatology found traction alopecia in an estimated 17 percent of African American women surveyed, and the authors note true prevalence is likely higher because many women don't seek diagnosis until the later stages [4].
If your temples look smooth and almost reflective with no visible follicle openings, book a board-certified dermatologist or trichologist. Products and routines cannot reverse scarring, and no edge growth product should claim otherwise. What a routine can do is protect the follicles that still work and give dormant-but-undamaged follicles a chance to recover.
How do you build a daily edge care routine for fine hair?
The daily routine for fine textured edges runs on one rule: least intervention, most protection. Every product application, every styling pass, every tight elastic is a withdrawal from your edge's health account. Fine hair starts with a smaller account.
Morning: begin with clean, dry or barely damp hands. If your edges look dry, put one pea-sized drop of a lightweight oil on your fingertips and press it, don't rub it, along the hairline. Oils that absorb without heavy residue suit fine hair: jojoba closely mimics the scalp's natural sebum, peppermint oil in diluted form (2 percent in a carrier) has some evidence for circulation support, and argan sits well without weight [5]. Castor oil, the community favorite, is too heavy for many fine hairlines. It can clog follicles or leave buildup that attracts more tension every time you pull the hair back.
If you have to style your edges, use the least hold that does the job. A light edge control gel with a soft bristle brush beats a heavy pomade slicked down with a dense boar-bristle brush and a lot of pressure. Smooth in one direction, leave it, and don't go over the same section more than twice.
Evening: take your hair down from any pulled style. Sleeping in a tight puff or bun adds hours of tension to follicles that should be resting. Wrap your edges gently in a silk or satin scarf, or use a satin-lined bonnet. Cotton pillowcases pull moisture from fine strands and create enough friction to snap them at the hairline.
That's honestly the whole daily routine. The urge to pile on multiple products twice a day is common and counterproductive for fine edges: buildup adds weight, weight increases mechanical force on fine follicles, and some ingredient combinations flake, which makes you brush them out, which creates more friction.
What should a weekly edge care routine include for fine textured hair?
Once a week, usually on wash day, is when the real work happens.
Cleanse the scalp at the hairline directly. Plenty of women skip the edges on wash day to save a style or because they're scared to disturb regrowth. That's backward. A clean scalp is a healthy scalp. Buildup of sebum, product residue, and sweat clogs follicles and drives inflammation [6]. Use a sulfate-free or low-sulfate shampoo (sulfates don't cause hair loss, but they strip the lipid layer from fine strands and leave them more breakage-prone in the days after washing). Apply shampoo along the hairline with your fingertips, not your nails. Gentle circular motions with fingertip pads move blood and dislodge debris without traumatizing the follicle.
Scalp massage deserves more credit than it gets. A small randomized controlled trial published in ePlasty in 2016 found that 4 minutes of standardized scalp massage per day over 24 weeks increased hair shaft thickness in participants [7]. That study used a standardized massage device, so the exact translation to fingertip massage isn't nailed down, but the mechanism (more blood flow, mechanical stretching of dermal papilla cells) makes biological sense. For fine textured hair, a 5-minute massage on wash day, focused on the hairline and temples, is a low-risk add with reasonable support behind it.
After cleansing, apply a moisturizing conditioner and, if your routine includes it, a deep conditioning treatment. Keep the conditioner on the strands rather than the scalp so you don't block follicles. Rinse thoroughly. Then apply a lightweight leave-in to damp edges before styling.
Once a week, assess your edges honestly. Are they growing? Are the baby hairs along your hairline getting longer? Any new stubble-like hairs at the temples? A simple photo log every 2 weeks gives you real data instead of a guess.
Which ingredients actually help fine edges grow back?
The honest answer: research on ingredients for edge regrowth specifically is thin. Most studies look at scalp hair in general, and very few look at the hairline. Here's what has the most evidence behind it, with realistic expectations attached.
Minoxidil (2% or 5%) is the only topical with FDA clearance for androgenetic hair loss in women, and some dermatologists use it off-label for early-stage traction alopecia [8]. It works by extending the anagen (active growth) phase of the hair cycle. It's a drug, not a cosmetic, and it needs continued use to hold results. You won't find it in a cosmetic edge control product.
Peppermint oil at 3 percent was compared to 3 percent minoxidil in a 2014 animal study and produced comparable follicle depth and hair count increases [5]. One animal study is a real limitation, but diluted peppermint oil as a scalp treatment is low risk and widely used. Never apply it undiluted. Essential oils at full strength irritate skin and can worsen inflammation.
Biotin gets enormous attention. Supplementation only helps hair growth if you have a true biotin deficiency, which is uncommon in adults eating a varied diet. The NIH notes that most biotin-for-hair claims aren't supported by clinical evidence in people with adequate nutrition [9]. If your diet is severely restricted, a blood panel (biotin, iron, ferritin, vitamin D, zinc) is worth discussing with your doctor before you spend money on supplements.
Castor oil is probably the single most repeated edge recommendation in the natural hair community. No clinical trial supports it for hair regrowth. What it does well: it's a humectant, it seals moisture, and its viscosity makes fine strands look thicker for a while. For fine edges, use it sparingly, cut into a lighter carrier oil, so you get the moisture without the weight.
Edge Naturale's edge growth products, for reference, build their ingredient combinations around scalp health and follicle support rather than styling hold. If you want products formulated for regrowth instead of just laying edges, that's the category to look in.
The table below compares the evidence level for commonly cited edge growth ingredients.
| Minoxidil (FDA-cleared for women's hair loss) | 5 |
| Peppermint oil 3% (one animal RCT vs. minoxidil) | 2 |
| Scalp massage (one human RCT, shaft thickness) | 2 |
| Biotin supplement (evidence only for deficiency) | 1 |
| Castor oil (no clinical trials for regrowth) | 0 |
Source: NIH PubMed Central, AAD, NIH ODS (see citations 2, 5, 8, 9)
What styling habits do the most damage to fine textured edges?
Styling is where most edge damage actually happens. The habits below are the ones dermatology research ties directly to traction alopecia and edge breakage [2] [3].
Tight braids, twists, and locs pulled to the scalp are the most documented cause of traction alopecia. "Repeated tension on hair follicles can cause a specific type of hair loss called traction alopecia," according to the American Academy of Dermatology's guidance on hair loss [2]. The tension doesn't have to hurt to do damage. Chronic low-grade tension over months causes the same follicle damage as sharp, painful tension, just more slowly.
Elastics placed directly on the hairline are a separate category. The elastic catches on fine strands and snaps them at the point of contact. Fabric-covered elastics do less damage than bare rubber, but any elastic set at the same spot repeatedly builds a line of breakage. Look at where you tie your hair back every day and see if your breakage pattern maps to exactly that spot. It usually does.
Heavy product buildup that gets combed or brushed out creates a mechanical breakage loop. Heavy gel or pomade stiffens fine edges; when you re-smooth them, you're applying shear force to strands locked in place. The strand breaks instead of bending. That's why fine edges need lighter-hold products that move with the hair rather than freezing it.
Heat tools on the hairline are an underrated damage source. Flat irons and hot combs on fine strands strip moisture and weaken the protein bonds in the shaft. Repeated heat without adequate protein treatment leads to what's sometimes called hygral fatigue or heat damage: strands that are limp, stretchy, and snap under barely any force.
Restyling frequency matters too. Re-laying your edges every morning with a brush and gel means daily mechanical tension on the follicle. Some styles do better with a once-set, leave-it-alone approach for 3 to 4 days, especially while your edges are trying to recover.
What protective styles are actually safe for fine edges?
Protective styles are supposed to cut manipulation and tension. Installed wrong, they do the opposite. For fine textured edges, how the style goes in matters as much as which style you pick.
Loose twists and braids installed without tension at the root are genuinely protective. The thing that makes a style safe isn't the type of braid, it's how much pull sits at the scalp. If you can feel the pull, it's too tight. Full stop.
Wigs and half-wigs with adjustable straps, rather than glued lace fronts, are among the best options for thinning edges. They take tension off the hairline entirely and let the follicles rest. The caveat: wig caps that compress the hairline, plus the glues and tapes used for lace fronts, can cause their own damage with constant use. A wig worn 5 days on, 2 days off with proper edge care underneath is a different animal than a glued lace front worn around the clock.
Bantu knots, two-strand twists, and flat twists on freshly washed, detangled hair without excessive pulling are reasonable choices. The detail that matters is how you secure them at the base. Finger-coiling instead of tight pinning cuts tension on the follicle.
The styles to skip during active regrowth: high-tension ponytails, sleek buns pulled tight from the hairline, sewn-in weaves with tight braided bases along the perimeter, and lace fronts with frequent glue. None of these are banned forever. They're just the wrong call while your edges are in a recovery phase.
For products that pair with protective styling without weighing down fine strands, the she is bomb edge control review covers how popular edge controls perform across different hair densities.
How long does edge regrowth take for fine textured hair?
Everyone wants this answered with a single number. The honest answer is a range with a lot of individual variation.
The hair growth cycle runs in three phases: anagen (active growth, 2 to 6 years on top of the scalp, shorter at the hairline), catagen (transition, 2 to 3 weeks), and telogen (rest and shedding, 2 to 3 months) [1]. Hairline follicles naturally have shorter anagen phases than mid-scalp follicles, which is part of why your edges never grow as long as the rest of your hair.
For follicles that are dormant but not permanently damaged, visible regrowth usually starts within 3 to 6 months of removing the damage source. Getting back to your previous density can take 12 to 24 months. Fine strands look slower to recover because even the new growth is thin and easy to miss until there's real density.
For follicles with scarring (late-stage traction alopecia), regrowth isn't possible, because the follicle structure has been replaced by fibrous tissue. That's why early intervention matters so much. No topical, prescription minoxidil included, grows hair from a follicle that no longer exists.
If you've held a lower-tension routine for 6 months and see nothing, that's your signal to book a dermatologist. A scalp biopsy can tell dormant follicles from scarred ones, and that difference changes everything about which treatments make sense [3].
What products should you actually use (and skip) for fine edges?
The product shelf for edges is enormous and mostly built for hold, not health. Here's a practical framework for fine textured edges.
Use: lightweight water-based gels or creams with flexible hold. Aloe vera gel, glycerin, and light plant-based oils give enough control for everyday styles without the rigidity that causes breakage during restyling. Look for products that stay pliable rather than crunchy when dry.
Use: scalp serums with nourishing or circulation-supporting ingredients, applied at the hairline before bed on nights when your hair is down. They absorb overnight without adding styling weight.
Use: a soft-bristle edge brush or a toothbrush-style styling brush. Boar bristle brushes with stiff, dense bristles generate more friction and pulling force than fine strands at the hairline need.
Skip: heavy pomades and waxes as a daily product. They build up fast, attract lint and debris, and take more mechanical effort to remove, which feeds the brush-and-breakage loop.
Skip: products with high concentrations of alcohol as a main ingredient. Drying alcohols (isopropyl alcohol, ethanol as a first or second ingredient) pull moisture from fine strands and leave them brittle.
Skip: extreme-hold edge tamers while you're in a recovery phase. Maximum-hold products chase the cosmetic result (a slicked, shiny hairline) over follicle health. You can always go back to them once your edges have recovered some density.
Edge Naturale's product collection at edgenaturale.com is worth a browse if you want products formulated for regrowth support rather than styling. The gap between a styling product and a treatment product is real, even when the packaging blurs it.
How does scalp health affect edge regrowth for fine hair?
Your scalp is where hair growth actually happens. Products on the strand itself can't reach the follicle. Only products on the scalp interact with the living cells that make hair.
Scalp inflammation is one of the most underrated drivers of edge thinning. Seborrheic dermatitis (dandruff), contact dermatitis from product reactions, and folliculitis (follicle infection) all wreck the follicle's ability to produce healthy hair. If your scalp is consistently itchy, flaky, or tender along the hairline, that inflammation needs treatment before any edge growth routine will work well.
Blood flow to the scalp delivers the oxygen and nutrients follicles need. That's the mechanism behind scalp massage, and it's also why smoking, poor sleep, and high chronic stress drag on hair growth systemically. The follicle is a metabolically busy structure; anything that restricts blood flow or raises systemic inflammation reaches it [6].
Scalp hydration is separate from strand hydration, though related. A dry scalp can signal over-washing, under-washing (buildup that irritates the skin), contact reactions, or dry weather. Fine textured hair often stretches the time between washes to cut manipulation, but the scalp itself doesn't gain from going long without cleansing. A targeted scalp spray of water and a little lightweight oil between wash days hydrates the scalp without wrecking a set style.
The NIH's National Institute of Arthritis and Musculoskeletal and Skin Diseases points to proper scalp care and avoiding chemical or physical damage as the main preventive strategies against non-genetic hair loss [10]. For fine textured edges that isn't abstract. It maps straight to: cleanse regularly, cut tension, treat inflammation early.
Can diet and supplements help fine edges grow back?
Diet affects hair growth, but mostly when there's an actual deficiency. Hair follicles are among the fastest-dividing cells in the body, and they need a steady micronutrient supply to keep that pace.
Iron deficiency is the most common nutritional cause of hair loss in women, and it's especially common in women of reproductive age. Ferritin (stored iron) below 30 nanograms per milliliter is linked to increased shedding, and some dermatologists push ferritin to at least 70 ng/mL for hair loss patients, though the exact threshold is still argued in the literature [11]. Get a blood panel. Don't guess.
Vitamin D deficiency also ties to hair loss through its role in follicle cycling. Vitamin D receptors sit in hair follicles, and low vitamin D links to alopecia areata and general shedding [11]. Since vitamin D deficiency runs high in Black Americans because of melanin's effect on UV absorption, this one is worth checking specifically.
Zinc and protein are two more nutrients where deficiency shows up in the hair. Crash diets and very low protein intake trigger diffuse shedding within 3 to 6 months of the change (telogen effluvium). If your shedding kicked in after a big dietary shift, that timeline is a useful clue [1].
For most people eating a reasonably varied diet, expensive multi-ingredient hair growth supplement stacks won't produce noticeable results. The nature's bounty hair growth page covers one popular option if you want details on a specific product. A basic blood panel is a better first investment than supplements.
When should you see a dermatologist about your edges?
A good routine handles the common, reversible causes of edge thinning. A dermatologist handles the rest.
See a dermatologist if your edges have thinned progressively for more than 6 months with no obvious styling cause; if there's smooth, shiny skin at the hairline with no visible follicle openings; if you have persistent itching, pain, or burning at the hairline; if small pustules or crusting appear along the hairline; or if a first-degree relative has significant hair loss (which raises the odds of a genetic component).
A dermatologist can do a scalp dermoscopy (a magnified view of the scalp that shows follicle structure without cutting) or a punch biopsy, which gives definitive information about whether follicles are dormant or scarred. That distinction determines whether any growth is possible and which treatments fit [3].
Traction alopecia caught in the early inflammatory phase can be treated with topical or injected corticosteroids to calm inflammation, and sometimes with minoxidil to try to extend the anagen phase of recovering follicles [8]. Late-stage traction alopecia with fibrosis is sometimes a candidate for hair transplant surgery, though that's a separate conversation needing specialist evaluation.
Don't wait until the damage is obvious. Smooth skin at the temple is late-stage. Fragile, receding hairline hairs that you can still see but that look shorter every month are early-stage, and that's the time to act.
Frequently asked questions
What is the best daily routine for fine textured edges?
Morning: press one pea-sized drop of a lightweight oil (jojoba or argan) gently along the hairline. Style with a light-hold water-based gel and a soft brush using minimal passes. Evening: take your hair down from any pulled style, and sleep in a silk or satin bonnet or on a satin pillowcase. That's genuinely all a daily routine needs to be for fine edges. More intervention usually means more damage.
How can I tell if my edge loss is from traction alopecia or something else?
Traction alopecia follows your styling habits: hairline recession at the temples, forehead, and nape where styles pull hardest. Alopecia areata tends to show up in round patches anywhere on the scalp. Androgenetic hair loss in women usually thins the crown, not the hairline. If you're unsure, a dermatologist can distinguish causes with a dermoscopy exam and sometimes a biopsy.
Is castor oil actually good for fine edges?
No clinical trial supports castor oil specifically for hair regrowth. It moisturizes and temporarily thickens the look of fine strands because of its viscosity. For fine edges it's often too heavy alone and can cause follicle-clogging buildup. Mix a small amount into a lighter carrier oil like jojoba instead of applying it straight. It's not harmful in moderation, but it's also not a regrowth treatment.
How often should I wash my edges if they're thinning?
Once a week works for most people with thinning fine edges. Cleansing clears buildup that clogs follicles and feeds scalp inflammation. The worry about washing too often is really about over-manipulation, not the water or shampoo itself. Use a sulfate-free shampoo, apply it with fingertip pads (not nails), and let your scalp and edges dry before styling.
What protective styles are safe when your edges are already thin?
Loose twists and braids installed without tension at the root, wigs with adjustable straps worn over a protected natural style, and bantu knots secured without tight pinning are the safest options. Avoid high ponytails, slicked-back buns, and glued lace front wigs at the hairline during active recovery. Installation tension matters far more than the style type itself.
How long does it take for fine textured edges to grow back?
For follicles that are dormant but undamaged, visible regrowth usually starts within 3 to 6 months of removing the tension source. Full density recovery can take 12 to 24 months. Fine strands are harder to spot until meaningful density builds, so photo logs every 2 weeks beat daily visual checks. Follicles with permanent scarring from late-stage traction alopecia do not regrow.
What ingredients should I avoid in edge products if I have fine hair?
Avoid heavy waxes and petroleum-based pomades as daily products; they build up and need aggressive mechanical removal. Avoid high concentrations of drying alcohols (isopropyl alcohol or ethanol near the top of the ingredient list) because they strip moisture from fine strands. Maximum-hold gels that dry rigid rather than flexible cause breakage when you restyle. Fragrance-heavy products can also trigger scalp contact dermatitis.
Can scalp massage really help edge regrowth?
A small 2016 randomized controlled trial in ePlasty found that 4 minutes of daily standardized scalp massage over 24 weeks produced measurable increases in hair shaft thickness. The mechanism is more blood flow and mechanical stimulation of dermal papilla cells. The study didn't focus on the hairline, and fingertip massage hasn't been directly compared to device massage, but it's a low-risk practice worth adding to a weekly routine.
Does what I eat affect my edges growing back?
Yes, when there's a deficiency. Iron (specifically ferritin), vitamin D, zinc, and adequate protein all affect follicle function. Deficiencies in these link to increased shedding and slower regrowth. The effect matters mainly when you actually have a deficiency, not as a baseline booster if your levels are normal. Get a blood panel before spending money on supplements.
Are silk scarves actually worth using at night for fine edges?
Yes. Cotton creates friction that snaps fine strands with their thinner cuticle layer. A silk or satin bonnet or pillowcase cuts friction and moisture loss overnight. You're in contact with your pillow for 6 to 8 hours, so the material matters. It's one of the higher-return, lower-cost changes in an edge care routine, usually under $15 for a bonnet.
When should I stop trying home remedies and see a dermatologist?
See a dermatologist if thinning has continued for 6 or more months with no clear styling cause, if you have smooth shiny skin at the temples with no visible follicle openings, if there's persistent pain or itching at the hairline, or if you have folliculitis symptoms (pustules, crusting). A scalp dermoscopy or biopsy can separate dormant follicles from scarred ones, which changes the entire treatment conversation.
Is it safe to use edge control products every day on fine hair?
Daily edge control is safe only if the product is lightweight, the application is minimal, and you cleanse your scalp at least weekly. The risk of daily product use on fine edges is cumulative buildup, which adds weight, invites more mechanical manipulation to remove, and can clog follicles over time. A light-hold water-based product applied sparingly beats a heavy gel applied generously.
What's the difference between edge breakage and edge shedding?
Shed hairs have a visible white bulb at the root; they've completed their growth cycle and released from the follicle. Broken hairs snap mid-shaft with no bulb; they've been physically severed by tension, friction, or dryness. Thinning edges from traction alopecia involve both, but the earliest visible evidence is usually short broken hairs along the hairline, not bulb-bearing shed hairs.
Sources
- NIH National Library of Medicine, StatPearls: Hair Follicle Anatomy and Physiology: Hair growth cycle phases (anagen, catagen, telogen) and follicle anatomy including cuticle structure and strand diameter differences
- American Academy of Dermatology, Hairstyles That Pull Can Cause Hair Loss: Repeated tension on hair follicles causes traction alopecia, which begins as reversible inflammation and can progress to permanent scarring
- American Academy of Dermatology, Hair Loss: Diagnosis and Treatment: Late-stage traction alopecia with follicle scarring does not respond to topical treatments; scalp biopsy distinguishes scarred from dormant follicles
- Journal of the American Academy of Dermatology, Traction Alopecia Prevalence Study (Haskin & Aguh, 2016): An estimated 17 percent of African American women surveyed showed evidence of traction alopecia; authors note actual prevalence is likely higher due to underreporting
- NIH PubMed Central, Peppermint Oil Promotes Hair Growth Without Toxic Signs (Oh et al., 2014, Toxicological Research): 3 percent peppermint oil solution produced comparable hair follicle depth and hair count increases to 3 percent minoxidil in an animal model
- NIH PubMed Central, The Role of the Scalp Microbiome and Inflammation in Hair Health: Sebum and product buildup can clog follicles and drive scalp inflammation that impairs follicle function
- NIH PubMed Central, Standardized Scalp Massage Results in Increased Hair Thickness (Koyama et al., 2016, ePlasty): 4 minutes of daily standardized scalp massage over 24 weeks led to measurable increases in hair shaft thickness in participants
- NIH PubMed Central, Traction Alopecia: The Root of the Problem (Samrao et al., Clinical and Experimental Dermatology): Minoxidil is used off-label for early-stage traction alopecia; topical or injected corticosteroids address inflammation in the early inflammatory phase
- NIH Office of Dietary Supplements, Biotin Fact Sheet for Health Professionals: Biotin supplementation supports hair growth only when a true biotin deficiency exists; evidence for benefit in people with adequate nutritional status is not established
- NIH National Institute of Arthritis and Musculoskeletal and Skin Diseases, Hair Loss (Alopecia Areata) Overview: Proper scalp care and avoiding chemical or physical damage to hair follicles are primary preventive strategies against non-genetic hair loss
- NIH PubMed Central, The Role of Vitamins and Minerals in Hair Loss: A Review (Almohanna et al., 2019, Dermatology and Therapy): Iron deficiency (low ferritin) and vitamin D deficiency are associated with hair shedding and impaired regrowth; vitamin D receptors are present in hair follicles