Natural hair growth products that actually work (and what doesn't)

Last updated 2026-07-09

What does the research actually say about natural hair growth?

Hair growth research is messier than the beauty aisle lets on. You get a handful of randomized controlled trials on natural ingredients, a much bigger pile of in-vitro (lab dish) studies that tell you almost nothing about your actual scalp, and a huge gray zone of traditional use that nobody has ever tested formally. That gap matters. "Clinically proven" on a bottle can mean one lab study with 20 people and no control group.

Here is what we know with reasonable confidence. Human scalp hair grows roughly 0.35 mm per day, or about half an inch a month on average ^[1]. That rate is partly genetic, partly hormonal, partly nutritional, and heavily affected by scalp health and mechanical stress. No topical product overrides your genetics. What products can do is reduce breakage (which makes length retention look like growth), improve scalp circulation, calm inflammation, or fix a deficiency that is slowing your natural rate.

The American Academy of Dermatology draws a clean line between treatments with evidence and those without ^[2]. Among natural topical ingredients, rosemary oil has the strongest human trial data right now. A 2015 randomized controlled trial in Skinmed compared rosemary oil to minoxidil 2% over six months in patients with androgenetic alopecia. Both groups saw "a significant increase in hair count at the six-month endpoint," and scalp itching was actually less common in the rosemary group ^[3]. That single study does not prove rosemary works for every hair loss type, and the sample was 100 people, all with androgenetic alopecia. Still a real result.

Everything else sits below that bar. Some ingredients have a plausible mechanism (caffeine, pumpkin seed oil, topical melatonin). Some have traditional use across cultures but zero RCT data (castor oil, black seed oil, fenugreek). And some are riding marketing momentum with almost nothing behind them.

Which natural oils are actually good for hair growth?

Not all oils do the same job. Some penetrate the shaft and reduce protein loss (coconut oil, avocado oil). Some work on the scalp by affecting circulation or DHT activity. Some just coat the surface and add slip. Knowing which bucket an oil falls into tells you how to use it.

Rosemary oil is the front-runner for topical scalp use. Its active compound, rosmarinic acid, may block 5-alpha-reductase (the enzyme that converts testosterone to DHT, the hormone tied to follicle miniaturization) and lift circulation to the scalp ^[3]. If you try one oil specifically for growth, make it this one. There is a full walkthrough on dilution and application in this guide to rosemary oil for hair growth, and if you want to mix your own serum, see how to make rosemary oil for hair.

Pumpkin seed oil has one randomized controlled trial behind it, published in Evidence-Based Complementary and Alternative Medicine in 2014. Seventy-six men with androgenetic alopecia took 400 mg of pumpkin seed oil daily (oral, not topical) for 24 weeks. The treatment group showed a 40% jump in hair count against 10% in placebo ^[4]. That was an oral dose, not a scalp treatment, and it was men only, so read the extrapolation carefully.

Castor oil is the most beloved oil in the natural hair community and it has almost no clinical trial data. What it has is a high ricinoleic acid content (anti-inflammatory in lab studies) and a thick viscosity that coats strands and cuts breakage. Less breakage looks like growth because your length stays on your head. It is not a fraud. It is just not doing what most people think it does.

Coconut oil reduces protein loss from hair more than mineral oil or sunflower oil in lab studies, which matters for textured hair that is prone to hygral fatigue and snapping ^[5]. Breakage reduction equals better length retention. Real benefit, even though coconut oil is not stimulating a single follicle.

Here is a quick comparison of the most-used natural oils:

Oil	Main mechanism	Human trial data?	Best use
Rosemary oil	Scalp circulation, possible DHT inhibition	Yes (1 RCT, topical) [3]	Scalp massage, serum
Pumpkin seed oil	Possible DHT inhibition	Yes (1 RCT, oral) [4]	Supplement or scalp use
Castor oil	Anti-inflammatory, coats shaft	No RCT	Sealing, scalp massage
Coconut oil	Reduces protein loss	Lab studies only [5]	Pre-shampoo, sealant
Black seed oil	Anti-inflammatory, antioxidant	Mostly animal/lab data	Scalp oil
Peppermint oil	Vasodilation, increased circulation	1 mouse study [6]	Scalp massage (diluted)

Peppermint oil's data comes mostly from a 2014 mouse study that found more dermal thickness and follicle number ^[6]. Compelling enough to mention, not enough to call proven in humans. Dilute it to 1-2% in a carrier oil, because undiluted peppermint on your scalp burns.

For more on which essential oils for natural hair growth hold up, that guide goes deeper on dilution ratios and safety.

What are the best natural hair growth products for textured hair specifically?

Textured hair has structural quirks that change the math. 4C hair has more points of potential breakage per inch than straight hair, because the curl pattern itself creates weak points. The cuticle sits differently. Moisture stays harder to hold. And the styling common in the natural hair community (tight braids, weaves, locs, repeated tension at the hairline) creates a specific set of risks any growth routine has to plan around.

So "best" for natural hair means products that support the scalp without clogging follicles, cut breakage alongside any growth benefit, and do not leave buildup that undoes your progress.

Scalp serums with rosemary oil, caffeine, or niacinamide clear that bar better than heavy butters slathered on the scalp. Heavy products at the roots can block follicles over time and feed folliculitis (scalp inflammation that shows up as small, sometimes painful bumps). Keep the thick butters on your strands.

Topical caffeine has genuinely interesting data. A 2007 study in the International Journal of Dermatology found caffeine penetrates the hair follicle and may counter the growth-suppressing effect of testosterone on follicles in lab conditions ^[7]. Caffeine scalp treatments are cheap, low-risk, and plausible enough to try.

Edge Naturale makes a line built for the edges and hairline, the zone most vulnerable to traction alopecia during protective styling. If you are thinning at the perimeter, a product designed for that exact area beats a general-purpose oil.

For the body and length of your hair, the goal shifts to moisture and breakage prevention. This is where a solid hair breakage guide matters as much as any growth product list.

The best products for natural hair growth tend to share a few traits: light enough to use on the scalp consistently, at least one ingredient with a real mechanism, and no need for daily manipulation to apply (daily fiddling at the edges is its own kind of damage).

Rosemary oil (topical, 6 mo)	10.2
Minoxidil 2% (topical, 6 mo)	9.9
Rosemary oil (3 mo interim)	3.1
Minoxidil 2% (3 mo interim)	3.0

Source: Panahi et al., Skinmed, 2015 (PMID 25842469)

How does scalp massage fit into a natural hair growth routine?

Scalp massage might be the most underrated free tool in a growth routine, and it has an actual clinical study behind it.

A 2016 study by Koyama et al. in Eplasty had nine healthy Japanese men do 4 minutes of standardized scalp massage daily for 24 weeks. Hair thickness rose from 0.085 mm to 0.092 mm on average ^[8]. The researchers proposed that mechanical stretching of dermal papilla cells switched on hair growth genes. Small study, no control group, so not definitive. But it costs nothing and the mechanism holds up.

For your edges, use light fingertip massage (not nails) in small circles for a few minutes a day. That may raise blood flow to follicles squeezed flat by tight styles. Pair it with a diluted rosemary or peppermint blend if you want to stack the benefits.

One thing to skip: aggressive brushing or combing at the hairline to "stimulate" growth. That is the opposite of what you want. Tension and friction on already-thin edges speed the problem up. Traction alopecia walks through exactly how that damage stacks and what reversal looks like.

Can nutritional deficiencies cause hair loss and do supplements help?

Yes. Certain deficiencies cause real, measurable hair loss, and correcting them with the right supplement absolutely helps. Only if you actually have the deficiency, though.

Iron deficiency is one of the most common reversible causes of hair loss in women, especially women with heavy periods. Ferritin (stored iron) below 30 ng/mL tracks with hair loss in some research, though dermatologists often name 70 ng/mL as a better target for hair specifically ^[2]. Test your ferritin before you take iron. Excess iron is toxic.

Vitamin D deficiency has a documented link to alopecia areata and telogen effluvium (diffuse shedding). The NIH Office of Dietary Supplements notes that vitamin D receptors sit in hair follicles, and low levels show up across multiple alopecia studies ^[9]. Supplementing if you are low is reasonable. Supplementing when your levels are fine grows nothing.

Biotin (vitamin B7) gets marketed hard for hair. The evidence for biotin in people without a deficiency is extremely thin. A 2017 review in Skin Appendage Disorders found that every published case showing improvement with biotin involved an underlying deficiency or metabolic disorder ^[10]. Most people eating a varied diet are not biotin deficient. And if your shampoo or oil says "with biotin," know that biotin does not absorb through skin or hair in any meaningful way.

Zinc and selenium deficiencies also link to hair loss. Same rule: supplementing helps if you are low, and oversupplementing can cause hair loss (selenium toxicity is real).

The honest take: before you buy a supplement stack, get bloodwork. Test ferritin, vitamin D, thyroid (TSH, free T3, T4), and a complete blood count. If everything is normal and you are still shedding, the supplement aisle probably will not change that. If something is off, fixing it might be the single most effective thing you do.

How does traction alopecia affect edges and can it be reversed naturally?

Traction alopecia is hair loss from repeated mechanical tension on the follicle. It hits Black women disproportionately because of styling: tight braids, weaves, locs, sleek ponytails, and heavy extensions all create the chronic pull that wears follicles down over time ^[2].

The AAD describes the classic pattern as thinning along the hairline and temples, often with tiny pimples or scaling around the follicles in earlier stages. The good news: early-stage traction alopecia is often reversible once you remove the tension. The bad news: chronic, long-term traction scars follicles permanently, and at that point no topical product regrows hair, because there is no working follicle left to stimulate ^[2].

So the most useful thing you can do for your edges is take tension off the hairline. Looser braids, lighter extensions, wearing styles down more often, and choosing protective hairstyles that do not rely on sleek, gel-pulled edges.

For early recovery, some dermatologists recommend topical minoxidil (not a natural product, but the most evidence-backed option), anti-inflammatory scalp treatments, and removing the tension source as the main move. Natural add-ons like rosemary oil and scalp massage are reasonable, but they do not replace ending the pull that is causing the damage.

No topical product, natural or not, cures established traction alopecia. That claim is false. But supporting scalp health while follicles recover from reduced tension is genuinely useful.

What role does postpartum hair loss play, and do natural remedies help?

Postpartum hair loss (postpartum telogen effluvium) shows up two to four months after delivery and it can be scary. A large share of women see noticeable shedding, sometimes in handfuls. The cause is hormonal. Estrogen surges during pregnancy keep hair in the growth phase longer than usual, then drop sharply after delivery, pushing a big cohort of follicles into shedding all at once ^[1].

Here is the part that helps: postpartum hair loss is self-limiting in most cases. Hair typically returns to its pre-pregnancy baseline by the baby's first birthday, sometimes sooner ^[1]. You are not going bald. You are losing hair you would have shed over the past nine months, just compressed into a few weeks.

Natural remedies will not speed up the hormonal reset. They can help with the anxiety of watching it happen, and cutting breakage during this stretch is worth doing. Gentle handling, protective styles that spare the hairline, and making sure you are not depleted after birth (iron and vitamin D run low postpartum) are the practical steps. There is a fuller picture at postpartum hair loss.

If shedding runs past one year postpartum, or it is severe, see a dermatologist to rule out thyroid trouble or lingering iron deficiency.

What ingredients in hair growth products should you actually look for?

If you are holding a product and want to know whether it is worth trying, start with the ingredient label. Here is an honest tier list.

Tier 1: Some human evidence Rosemary leaf extract or Rosmarinus officinalis oil, caffeine, pumpkin seed oil (oral form), saw palmetto (may block 5-alpha-reductase; limited human data but a plausible mechanism).

Tier 2: Plausible mechanism, limited human data Peppermint oil (vasodilation, one animal study), black seed oil (Nigella sativa, anti-inflammatory, one small human study on alopecia areata), niacinamide (improves scalp microcirculation), ginseng extract (some in-vitro data on dermal papilla cells).

Tier 3: Probably just coating and marketing Biotin in topical formulas, collagen in shampoo, keratin in growth serums (keratin does not absorb; it fills surface gaps for a while). Not harmful. Just not stimulating follicles.

When a product lists its active ingredient last, or buries it in a ten-item list, the amount is probably too small to matter. A rosemary serum where rosemary sits third is a different product than one where it sits eighth.

Check the full list for scalp-clogging agents too (thick petrolatum, heavy waxes, silicones that build up) if you plan to apply straight to your scalp. For edges hair care, lighter almost always wins.

How long does it take to see results from natural hair growth products?

Longer than most products claim. The hair growth cycle runs in phases: anagen (active growth, 2 to 7 years), catagen (transition, a few weeks), and telogen (resting and shedding, roughly 3 months). A product that stimulates a follicle today shows nothing visible until that follicle cycles back into active growth.

In the rosemary versus minoxidil trial, significant results appeared at six months ^[3]. The pumpkin seed oil trial ran 24 weeks ^[4]. The scalp massage study ran 24 weeks ^[8]. The pattern holds: you are not judging anything meaningful before 16 weeks, and a fair verdict needs 24.

Growth timelines, rough averages:

• Edges and hairline: 0.3 to 0.5 mm per day if follicles are active. Barely visible regrowth to an inch of length takes about three months of undisturbed growth.
• Early traction alopecia reversal: some studies suggest 6 to 12 months of tension removal before real visible regrowth, if the follicles are not scarred.
• Postpartum shedding recovery: generally 6 to 12 months from delivery.

Anyone selling a natural product with "results in 30 days" photos is selling lighting and angles, not follicle biology. Give a real routine six months before you write it off or call it a win.

Are there natural remedies for hair growth that cost almost nothing?

Yes. And honestly, some of them beat expensive products on the evidence.

Scalp massage is free and has a clinical study ^[8]. Four minutes a day is the protocol from that trial. You can do it in the shower with conditioner on.

A rosemary oil DIY serum costs roughly $8 to $15 for a 2-ounce bottle (a 10 mL bottle of quality rosemary essential oil plus a carrier like jojoba runs under $15 total) and competes head-to-head with $40 to $60 branded serums that hold the same active. The full process is here: how to make rosemary oil for hair.

Taking tension off the hairline costs nothing and is one of the most evidence-supported moves for edge thinning. Loosen your braids one notch. Skip edge control products with alcohol that dry and snap fine hairline hairs. Sleep on a satin pillowcase (around $12 to $20 for a decent one). All low-cost, all meaningful.

Bloodwork to find and fix a real deficiency is often covered by insurance and is the highest-value step if something is genuinely wrong hormonally or nutritionally.

The expensive tier (PRP treatments, laser caps, prescription minoxidil) makes sense in some cases. But for most women dealing with slow growth or mild edge thinning, the cheap fundamentals done consistently beat spotty use of a $70 serum.

Edge Naturale's full product collection is at edgenaturale.com if you want the evidence-backed ingredients in a ready-to-use format, which is a fine choice when DIY is not your thing.

What ingredients or habits actually slow hair growth or damage edges?

This is the part marketing skips. Some common habits in textured hair care work against growth.

Tight styles at the hairline top the list. The American Academy of Dermatology names traction alopecia as preventable with looser styles ^[2]. One study estimated traction alopecia affects roughly 17% of Black women, one of the most common causes of hair loss in this group, though estimates vary widely across studies.

Alcohol-based styling products on the hairline dry out already-fragile edge hairs and make them brittle enough to snap. If your edge control or gel lists denatured alcohol or ethanol in the first five ingredients, it is a problem for daily use on thinning edges.

Overwashing strips the scalp's protective sebum. Buildup on the scalp blocks follicles and can trigger folliculitis. The right frequency varies by person, but scalp health lives in the balance between those two.

Heat at the hairline is real damage. Flat irons run right up to the edges, blow dryers aimed at the perimeter without a diffuser, and hot comb use all wreck the cuticle of fine hairline hairs that are already weaker than the hair further back.

Relaxers applied too close to the scalp cause burns and follicle damage. If you relax, a trained stylist who leaves a base and times the application is not optional.

Supplementing hard without knowing your levels can backfire. Excess vitamin A is a documented cause of hair loss ^[9]. Excess selenium causes diffuse shedding. More is not better.

How do you build a complete natural hair growth routine?

A routine that works has three layers: scalp, strand, and systemic. Most people obsess over one and neglect the rest.

Scalp layer (weekly or 2-3x per week): Apply a diluted rosemary oil or caffeine serum straight to the scalp, focusing on the hairline and any thinning spots. Massage 3 to 5 minutes with fingertip pressure. Let it sit at least 30 minutes before washing, or use an overnight leave-in. This is where the growth-stimulating work happens.

Strand layer (wash day plus protective styling): Pre-poo with coconut or avocado oil to cut protein loss during washing ^[5]. Use a sulfate-free or low-sulfate shampoo to keep the scalp healthy without stripping it. Deep condition weekly for elasticity (elastic strands break less). Seal with a light oil after moisturizing. Style protectively, ends tucked, hairline loose. Read through protective hairstyles to sort which options actually protect instead of creating new tension.

Systemic layer (ongoing): Get bloodwork to know your ferritin, vitamin D, and thyroid numbers. Fix anything low. Eat enough protein (hair is mostly keratin, a protein; too little dietary protein slows growth). Manage stress where you can, because chronic stress raises cortisol and pushes follicles toward telogen. Sleep. These sound generic, but they move the needle in ways no topical product makes up for.

Consistency over three to six months, not perfection, is what gets you results you can see.

Frequently asked questions

What is the most effective natural ingredient for hair growth?

Rosemary oil has the strongest human evidence of any natural topical ingredient. A 2015 randomized controlled trial found it matched minoxidil 2% for hair count increase over six months in people with androgenetic alopecia. That does not mean it works for every type of hair loss, but among natural options it is the one with the most credible data behind it.

Does castor oil actually grow hair?

There are no randomized controlled trials on castor oil and hair growth in humans. What castor oil likely does is reduce breakage (its thick texture coats the shaft and its ricinoleic acid is anti-inflammatory at the scalp). Less breakage equals better length retention, which reads as growth. It is low-risk and cheap, so it is reasonable to try. Just do not expect it to regrow bald spots.

How long does it take for natural hair growth products to work?

The clinical trials on rosemary oil and pumpkin seed oil both ran 24 weeks before showing significant results. You need at least 16 weeks to evaluate any topical growth product, and 24 weeks for a fair assessment. Anything claiming visible results in 30 days is working with lighting and angles, not follicle biology. Plan for a six-month commitment before deciding whether a product works.

Can I grow my edges back naturally after traction alopecia?

Early-stage traction alopecia is often reversible if you remove the tension source promptly. The AAD notes that follicle scarring from chronic traction becomes permanent over time. Natural approaches like rosemary oil, scalp massage, and anti-inflammatory scalp treatments can support recovery, but the single most important step is loosening styles at the hairline. See a dermatologist if edge shedding continues after several months of reduced tension.

Are biotin supplements good for natural hair growth?

Only if you are biotin deficient. A 2017 review in Skin Appendage Disorders found that every published case where biotin supplementation improved hair involved an underlying deficiency or metabolic disorder. Most people eating a varied diet have adequate biotin. Topical biotin in shampoos and serums does not penetrate the follicle in any meaningful way. If your biotin levels are normal, supplements will not speed up growth.

What vitamins should I take for natural hair growth?

None, unless bloodwork shows you are deficient in something. The vitamins most linked to hair loss when low are iron (ferritin below 30 to 70 ng/mL depending on the reference), vitamin D, zinc, and B12. Fix real deficiencies and hair often improves. Supplementing things that are not low is mostly expensive urine. Excess vitamin A and selenium can actually cause shedding, so more is not better.

Is scalp massage effective for hair growth?

A 2016 study (Koyama et al., Eplasty) had participants do four minutes of standardized scalp massage daily for 24 weeks and measured a significant increase in hair thickness. It is a small study with no control group, so it is not definitive, but scalp massage is free, low-risk, and the proposed mechanism (mechanical stimulation of dermal papilla cells) is reasonable. It is one of the few zero-cost interventions with any clinical backing.

What is the best natural hair growth remedy for postpartum shedding?

Postpartum telogen effluvium is hormonal and typically self-resolves by the baby's first birthday without intervention. Natural remedies will not speed up the hormonal reset. What helps: ruling out iron deficiency (common after delivery), gentle protective styling, and reducing manipulation of the hairline. If shedding continues past 12 months postpartum or is severe, get thyroid and ferritin checked before buying any growth product.

Can I use multiple natural growth oils at the same time?

Yes, but keep total oil light on the scalp. Layering too many heavy oils there creates buildup that can block follicles and cause folliculitis. A practical approach: pick one or two active oils (rosemary, peppermint) diluted in a carrier (jojoba is light and non-comedogenic), apply to the scalp, and save thicker sealants like castor oil for the strands only. Less is more on the scalp itself.

Do natural hair growth products work differently for 4C hair?

The follicle biology is the same regardless of texture, but application and absorption differ. The tight curl pattern of 4C hair means scalp sebum does not travel down the shaft easily, so the scalp runs drier. Products applied to the scalp also need to be light enough not to build up at the roots. The evidence for rosemary oil and caffeine applies to all hair types, but formulas marketed for natural hair are usually designed with these texture-specific needs in mind.

Are natural hair growth products safe to use on color-treated or relaxed hair?

Generally yes. Scalp-applied oils and serums with rosemary, caffeine, or peppermint are safe on chemically processed hair. Be cautious with essential oils that are not properly diluted, since they can irritate a sensitized scalp. Avoid high-alcohol products on relaxed or color-treated hair, because those textures are already more porous and prone to dryness. Always patch test a new product if your scalp is reactive.

What is the difference between hair growth and hair length retention?

Hair growth is the rate new hair emerges from the follicle (roughly half an inch a month on average). Length retention is how much of that hair you keep, meaning it does not break off before you notice. Most people's growth rate is fine; their breakage rate is the problem. Many natural hair products work by reducing breakage, which shows up as length gain. Knowing which problem you have changes which product you actually need.

How much rosemary oil should I use on my scalp?

The clinical trial used a diluted preparation applied to the scalp daily. Standard aromatherapy guidance recommends essential oils at 1 to 2% dilution in a carrier oil for scalp use (roughly 6 to 12 drops of essential oil per ounce of carrier). Undiluted essential oils can cause contact dermatitis and scalp irritation. Apply directly to the scalp, not the hair shaft, and massage in for 2 to 5 minutes.

Can tight braids cause permanent hair loss?

Yes, if the tension is chronic and sustained. The AAD notes that traction alopecia from repeated tight styles can cause permanent follicle scarring. Early-stage traction alopecia (follicle intact, just stressed) is often reversible with tension removal. Scar-stage traction alopecia is not reversible with topical products. This is why catching edge thinning early and changing styling habits promptly matters more than which growth product you pick.

Sources

1. StatPearls (NCBI Bookshelf), NIH: Hair Follicle Anatomy and Physiology: Human scalp hair grows roughly 0.35 mm per day on average; postpartum telogen effluvium typically resolves by 12 months postpartum
2. American Academy of Dermatology (AAD): Hair Loss Types and Traction Alopecia: Traction alopecia is preventable with looser styles; chronic traction can cause permanent follicle scarring; iron deficiency is a reversible cause of hair loss in women
3. Skinmed (2015): Rosemary Oil vs. Minoxidil 2% RCT, Panahi et al.: Rosemary oil matched minoxidil 2% for hair count increase at six months in androgenetic alopecia; the study stated 'a significant increase in hair count at the six-month endpoint' in both groups
4. Evidence-Based Complementary and Alternative Medicine (2014): Pumpkin Seed Oil RCT, Cho et al.: 400 mg daily oral pumpkin seed oil for 24 weeks produced a 40% increase in hair count vs 10% in placebo in men with androgenetic alopecia
5. Journal of Cosmetic Science (2003): Effect of mineral oil, sunflower oil, and coconut oil on prevention of hair damage, Rele & Mohile: Coconut oil reduced protein loss from hair more than mineral oil or sunflower oil due to its affinity for hair proteins
6. Toxicological Research (2014): Peppermint oil promotes hair growth, Oh et al.: Topical peppermint oil increased dermal thickness and follicle number in mice, proposed mechanism is vasodilation
7. International Journal of Dermatology (2007): Caffeine and hair follicle stimulation, Fischer et al.: Topical caffeine penetrates hair follicles and may counteract testosterone-induced suppression of hair follicle growth in vitro
8. Eplasty (2016): Standardized scalp massage and hair thickness, Koyama et al.: Four minutes of daily standardized scalp massage for 24 weeks increased hair strand thickness significantly from 0.085 mm to 0.092 mm
9. NIH Office of Dietary Supplements: Vitamin D Fact Sheet for Health Professionals: Vitamin D receptors are present in hair follicles; low vitamin D levels appear in multiple alopecia studies; excess vitamin A is a documented cause of hair loss
10. Skin Appendage Disorders (2017): Biotin review, Zempleni et al.: Every published case showing hair improvement with biotin supplementation involved an underlying deficiency or metabolic disorder; biotin supplementation without deficiency has no proven effect on hair growth