How to stimulate dormant follicles at the hairline

Last updated 2026-07-10

What does a dormant follicle actually mean?

A dormant follicle is one that has stopped pushing out a visible hair shaft but hasn't been destroyed. It's resting, not dead. Every follicle cycles through three phases: anagen (active growth), catagen (a short transition), and telogen (rest). When a follicle sits in telogen longer than it should, or gets shoved out of anagen by chronic tension or inflammation, that's what people mean by "dormant" ^[1].

The distinction changes everything about your options. A follicle that's alive but quiet can re-enter anagen with the right push. A follicle replaced by scar tissue cannot. The American Academy of Dermatology notes that early traction alopecia, where follicles are stressed but not yet fibrotic, is reversible if the tension comes off in time ^[2]. Late-stage traction alopecia, with follicular scarring, is permanent.

So how do you tell which stage you're in? Look for perifollicular inflammation, which is redness or tenderness around the follicle opening, or very short, fine vellus hairs in the thin area. Those baby hairs mean follicles are still cycling, just weakly. Skin that looks smooth and shiny with no visible opening usually signals scarring. When you can't tell, a dermatologist can do a scalp biopsy to settle it ^[2].

What causes hairline follicles to go dormant in the first place?

The hairline is the most mechanically vulnerable part of your scalp. The follicles at your temporal edges and baby-hair zone are finer and shallower than the ones on the rest of your head, so they react to stress fast and recover slow.

The biggest cause in Black women with textured hair is traction. Tight braids, weaves set with too much tension, bonded extensions, even a snug headband worn daily. All of it pulls the follicle over and over, chokes its blood supply, and eventually pushes it into early telogen. The AAD identifies traction alopecia as the leading cause of hairline loss in African American women ^[2]. The damage stacks up quietly, which is why the loss often shows up years into a styling habit instead of right away. For more on the condition itself, see our guide to traction alopecia.

Other causes include:

• Postpartum hormone shifts (estrogen drops sharply after delivery and pushes follicles into telogen all at once, with the hairline thinning most visibly) ^[3]
• Seborrheic dermatitis and psoriasis, which keep the scalp inflamed and interfere with follicle cycling
• Androgenetic alopecia, the genetic miniaturization pattern that affects roughly 50% of women by age 50 ^[4]
• Nutritional deficiencies, especially iron, ferritin, and vitamin D ^[5]
• Harsh chemical services stacked too close together without recovery time

If your thinning started within a year of giving birth, read postpartum hair loss, because the timeline and the fix both differ from traction-related loss.

Usually more than one cause is running at the same time. Someone might have naturally fine edges, plus years of tight styles, plus low ferritin from diet. Fix one thing and ignore the rest, and you plateau. That's the trap most people fall into.

Can dormant hairline follicles actually grow back?

Yes, with real limits. The research on traction alopecia reversal is encouraging early and sobering late. A 2019 review in the Journal of the American Academy of Dermatology found that patients who stopped the offending hairstyle early showed significant regrowth, while those with follicular scarring did not respond to treatment ^[6]. The review gave no single regrowth percentage because outcomes varied too widely, but the direction is consistent across the literature: the earlier you act, the better.

For androgenetic alopecia at the hairline, it's the same story. Minoxidil, the FDA-approved topical, has been shown in randomized controlled trials to raise hair count and regrow miniaturized hairs, but it works best in follicles that still have some function, not fully fibrosed ones ^[7].

Here's the honest read. If you can still see fine, wispy hairs at your hairline, or feel follicle openings under good light, you have live follicles worth treating. If your edges have been gone for more than a few years with zero regrowth, get a dermatologist to check for scarring before you spend time and money on topicals that can't reach a dead follicle.

Stopping traction (early-stage TA)	3
Scalp massage (daily 4 min)	6
Rosemary oil (2-3% dilution)	6
Minoxidil 2-5% topical	4
PRP (3-session course)	4
Correcting ferritin deficiency	6
Microneedling + minoxidil	3

Source: Skinmed 2015 (rosemary RCT), ePlasty 2016 (scalp massage), FDA minoxidil labeling, NIH NIAMS

How long does it take to see regrowth from dormant follicles?

Three to six months is the honest answer for early-stage follicles responding to treatment. That timeline comes straight from the hair cycle. Anagen takes time to restart after a follicle has been resting, and the new hair has to grow long enough to actually see.

Minoxidil trials usually measure outcomes at 16 weeks (about four months) for an early signal and at 48 weeks (about twelve months) for full efficacy ^[7]. Rosemary oil matched 2% minoxidil in a randomized trial at six months, with statistically significant hair-count gains but little visible change before the four-month mark ^[8].

Scalp massage studies measured hair thickness at 24 weeks ^[9]. Nutritional correction runs slower still: bringing ferritin from deficient up to optimal can take three to six months before the hair cycle even responds, then another three before you see growth.

Plan for a six-month committed trial of whatever you choose. Most people quit at eight weeks because they see nothing. That's right before the window when change usually starts. Quitting early is the single most common reason edge routines "fail."

What actually works to stimulate dormant follicles at the hairline?

Here's where the evidence splits off from the marketing. A handful of approaches have real support. The rest are plausible at best.

Scalp massage A small 2016 study in ePlasty had nine men do four minutes of standardized scalp massage daily for 24 weeks. Hair thickness rose significantly over that stretch, and the authors credited stretching of follicle cells and better circulation ^[9]. Four minutes, daily, along the edges. That's the protocol they actually tested. Use the pads of your fingers, never your nails, and work small circles along the hairline before and after washing.

Minoxidil This is the only FDA-approved topical for hair loss with broad evidence behind it. The 2% solution is approved for women; the 5% foam is used off-label and also has clinical support ^[7]. Applied to the hairline nightly, it stretches anagen and may wake dormant follicles in areas that aren't fibrosed yet. Two trade-offs matter: you have to keep using it or the gains reverse, and some people shed in the first four to six weeks as resting hairs get pushed out to make room for new anagen hairs. That shedding is normal and temporary.

Rosemary oil A 2015 randomized controlled trial in Skinmed compared rosemary oil to 2% minoxidil in 100 patients with androgenetic alopecia over six months ^[8]. Both groups showed comparable hair-count increases by the end, and rosemary caused significantly less scalp itching than minoxidil. The mechanism looks like better scalp microcirculation plus some inhibition of 5-alpha-reductase, the enzyme tied to androgenetic hair loss. Our guide to rosemary oil for hair growth covers dilution ratios and how to apply it. You can also make your own infusion; see how to make rosemary oil for hair.

Removing the cause No treatment holds if you keep the tight styles, the heavy edge products, or whatever put the follicle to sleep. This is not a minor point. Stopping traction alone has produced spontaneous regrowth in early-stage traction alopecia across multiple case series. Your body wants to grow hair. Sometimes the strongest thing you can do is get out of its way.

Protective styling with low tension Sounds obvious, but the details decide it. A protective style only protects if it doesn't pull the hairline to install. Box braids with your edges left out and no extensions at the perimeter, loose twists, or wigs with no glue at the hairline all qualify. High-tension sew-ins, cornrows braided tight to the scalp at the edges, and bonded lace frontals do not. Our protective hairstyles piece breaks down which styles actually pass.

Which ingredients are backed by evidence for hairline regrowth?

Ingredient	Evidence level	Key finding	Notes
Minoxidil (2% or 5%)	FDA-approved, multiple RCTs	Increases hair count; extends anagen	Requires ongoing use; see derm before starting
Rosemary oil	1 RCT (n=100)	Comparable to 2% minoxidil at 6 months [8]	Must be diluted; avoid undiluted on skin
Peppermint oil	1 RCT in mice, 1 small human study	Increased dermal thickness, follicle depth	Human evidence is thin; promising but preliminary
Castor oil	Anecdotal only	No controlled trials found	High viscosity; popular but lacks RCT support
Caffeine (topical)	2 RCTs	Penetrates scalp, may counter DHT effects at follicle [10]	Early signal; not yet replicated at hairline specifically
Biotin (oral)	Evidence only for deficiency	Corrects deficiency-caused loss; no benefit in replete patients [5]	Most people who aren't deficient see no effect
Iron/ferritin	Observational studies	Low ferritin linked to increased telogen shedding [5]	Get serum ferritin tested; optimal level is debated (many researchers suggest above 70 ng/mL)
Saw palmetto (topical)	1 small trial	Some hair density increase; DHT inhibition proposed	Less evidence than rosemary

A few honest calls on this table. Castor oil is everywhere in the natural hair community, and it's a fine moisturizer, but there are no controlled trials showing it regrows hair. I wouldn't spend money on a castor oil serum sold for edge regrowth when rosemary oil has an actual RCT behind it. Biotin supplements are just as over-marketed. Unless bloodwork confirms a deficiency, they're unlikely to do anything for your edges.

If you want a well-formulated natural product that combines several of these ingredients, Edge Naturale's natural hair growth products collection is worth a look. I'd still get your ferritin and vitamin D checked first, because no topical beats a systemic deficiency.

How should you actually apply treatments to the hairline?

Technique matters more than most people think, because the hairline follicles sit in a small, curved zone where the scalp is thinner than elsewhere.

For oil-based treatments like rosemary oil or a carrier-oil blend:

1. Dilute it. For rosemary essential oil, standard dermatology guidance suggests 2 to 3 drops per teaspoon of carrier oil (roughly 1 to 2% concentration). Undiluted, it can cause contact dermatitis ^[11]. 2. Apply straight to the scalp at the hairline, not to the hair shaft. The target is the follicle, not the strand. 3. Massage gently for 3 to 5 minutes with fingertip circles. Don't drag or scratch. 4. Leave it on at least 30 minutes, or overnight under a satin bonnet. 5. Apply 3 to 5 times a week, consistently, more than when you remember.

For minoxidil: 1. The hairline is an off-label zone for most studies (most trials tested the crown), so flag this with your dermatologist. 2. Apply 1 mL of solution or half a capful of foam with the dropper or your fingers to the dry hairline. 3. Let it dry fully before layering anything else. 4. Apply once daily (some formulas say twice; follow the label or your doctor). 5. Wash your hands after. Minoxidil can grow hair anywhere it touches skin.

For scalp massage: Do it on a dry or barely damp scalp, not a soaking one where you're more likely to snag and snap fragile new hairs. A lightweight oil during massage is fine but not required.

One warning: don't stack every active at once. Starting minoxidil, rosemary oil, and a DHT-blocking supplement in the same week makes it impossible to know what worked if you see results, or what irritated you if you don't. Pick one primary treatment, hold it steady for at least eight weeks, then add a second.

What should you stop doing to protect hairline follicles while they recover?

Regrowth and damage can happen at the same time, which is how people stay stuck for years. You can do everything right with your treatment and still lose ground to your styling habits.

Stop these now if your edges are thinning:

• Laying edges with hard-hold gels applied straight to the hairline every day. Pulling the hair taut to "slick" it keeps chronic tension on the follicle. Switch to a lighter hold or skip laying your edges during recovery. Our edge control guide covers products that hold without the concrete-stiff pull.
• Tight ponytails, buns, or any style where you feel a pull at the hairline. Tension should never feel uncomfortable.
• Glue-based wigs and lace frontals bonded at the edge. The adhesive removal alone can damage follicles and the skin barrier.
• Brushing or combing edges hard when dry. Baby hairs and new growth snap easily.
• Relaxers applied to the hairline with no protective base. The edges process faster than the rest of the scalp and burn more easily there.

Also worth rethinking: sleeping without a satin bonnet or satin pillowcase. Cotton creates friction that breaks fragile new growth before it can settle in.

Some of these are big changes, especially if tight styles sit at the center of your professional or social life. The regrowth timeline doesn't require you to look undone. It just requires that whatever you wear, the hairline is carrying no mechanical stress.

When should you see a dermatologist about thinning edges?

A board-certified dermatologist with experience in hair disorders is the right call in several situations. Some go by the phrase trichologist-trained dermatologist, but board certification is what you're checking for.

See one if:

• You've had hairline thinning for more than two years with no regrowth despite removing the cause
• The skin at your hairline looks shiny, smooth, and featureless with no visible follicle openings
• You have itching, burning, or pain at the hairline (this can signal an inflammatory alopecia like frontal fibrosing alopecia, which needs a biopsy to diagnose and a different treatment path) ^[2]
• You want prescription-strength options like topical spironolactone, platelet-rich plasma (PRP), or low-level laser therapy
• Your hair loss came on suddenly alongside fatigue, weight changes, or changes in your skin and nails

A scalp biopsy is the only way to definitively separate non-scarring traction alopecia (potentially reversible) from scarring alopecia (not reversible). If there's any doubt, push for the biopsy before you sink money into months of treatment.

The NIH's National Institute of Arthritis and Musculoskeletal and Skin Diseases describes traction alopecia as "a form of gradual hair loss, caused primarily by pulling force being applied to the hair" and notes that "when diagnosed early, discontinuing the causative hairstyle often allows for natural hair regrowth" ^[12].

Are there any in-office treatments that help dormant hairline follicles?

Yes, though the evidence varies and the costs sting, since most aren't covered by insurance.

Platelet-Rich Plasma (PRP) PRP means drawing your blood, spinning it in a centrifuge to concentrate the growth-factor-rich plasma, then injecting it into the scalp. Several small studies show gains in hair density and thickness, and a 2019 meta-analysis in Dermatologic Surgery found statistically significant improvements across studies ^[13]. Results aren't guaranteed. A typical course runs three sessions spaced four to six weeks apart, usually $1,500 to $3,000 total depending on the practice and where you live, though prices vary widely.

Low-Level Laser Therapy (LLLT) FDA-cleared devices (which is not the same as FDA-approved for treatment) like laser caps and combs have some evidence for improving density in androgenetic alopecia. A 2014 randomized trial in the American Journal of Clinical Dermatology found significant improvement in hair density with a 9-beam laser device versus a sham device ^[14]. In-office LLLT costs vary widely; at-home devices run roughly $200 to $800.

Microneedling Controlled micro-injuries to the scalp with a dermaroller or automated device can trigger wound-healing growth factors and may help topicals absorb better. A small 2013 RCT in the International Journal of Trichology found patients who combined microneedling with minoxidil had significantly better hair-count responses than those on minoxidil alone ^[13]. Study roller sizes for the scalp run 0.5 mm to 1.5 mm.

None of these replaces removing the underlying cause. They're add-ons to a solid base of damage prevention, scalp care, and the right topical.

What role does nutrition play in hairline regrowth?

Nutrition is probably the most underrated part of edge regrowth, and also the easiest to fix if a deficiency is present.

Ferritin (stored iron) is the nutrient most consistently tied to hair loss in women. A study in the Journal of the American Academy of Dermatology found low serum ferritin is associated with chronic telogen effluvium, the diffuse shedding type ^[5]. Many labs call ferritin "normal" above 12 to 15 ng/mL, but some hair researchers argue the threshold for the hair cycle to run well sits closer to 50 to 70 ng/mL. The honest answer is the optimal cutoff is still debated. If your ferritin is low-normal and your hair is shedding, raise iron supplementation with your doctor.

Vitamin D deficiency has also been linked to alopecia areata and chronic telogen effluvium in observational studies, though the causality isn't firmly settled ^[5]. The NIH Office of Dietary Supplements defines vitamin D deficiency as a serum 25-hydroxyvitamin D level below 20 ng/mL ^[15].

Zinc, vitamin B12, and getting enough protein round out the main concerns. You don't need a pricey hair supplement for any of this. Standard bloodwork from your primary care doctor or OB-GYN screens for most of it.

One practical note. If you supplement iron without a confirmed deficiency, you can do real harm. Iron toxicity is a genuine risk with over-supplementation. Get the blood test first.

The essential oils for natural hair growth article pairs well here if you want to match a solid nutritional base with the right topical.

How can you tell if your hairline treatment is actually working?

Progress is slow and easy to miss, which is exactly why tracking matters.

The most reliable low-tech method: photograph your hairline in the same light, same angle, every four weeks. Use your phone and a mirror, or have someone shoot it from straight in front of you. After three months, put the first and most recent photo side by side. Your brain adapts to gradual change so fast that real progress can be invisible day to day.

Signs dormant follicles are waking up:

• New fine, short hairs showing up where there were none
• The hairline looking "fuzzy" instead of sharply receded
• Existing baby hairs growing a little longer and a little thicker over months
• Less shedding of the baby hairs already there

Signs treatment isn't working, or damage is still going:

• The hairline keeps moving back
• New thin patches appear inside the existing hairline
• Existing fine hairs keep shedding without replacement

If you see no change at all after four to six months of consistent treatment with the cause removed, that's your cue to revisit whether scarring is present. A dermatologist can use dermoscopy (a magnified scalp scope) to look for follicular dropout before recommending a biopsy.

Frequently asked questions

Can hairline follicles grow back after years of thinning?

Sometimes, but the odds drop the longer the follicles have been dormant. Follicles that are quiet but structurally intact can re-enter growth with the right stimulus. Follicles replaced by scar tissue cannot. If your hairline has been thinning for more than two years with no recovery, see a dermatologist for dermoscopy or a biopsy before investing in long-term treatment. Early intervention always beats late intervention.

How do I know if my hairline follicles are dead or just dormant?

The clearest sign of a live but dormant follicle is visible vellus hairs, those fine, short, almost transparent hairs in the thin area. A follicle opening you can see or feel is also a good sign. Skin that looks smooth, shiny, and featureless with no hair opening usually means scarring. A dermatologist with a dermoscope can tell the difference far more reliably than you can on your own.

Does castor oil really regrow edges?

There are no randomized controlled trials showing castor oil regrows hair. It's thick, moisturizing, and popular in the natural hair community for legitimate reasons, but the evidence is entirely anecdotal. If you enjoy it and it makes your existing hair feel better, it's harmless. But if you're choosing between castor oil and rosemary oil for edge regrowth, rosemary has an actual RCT behind it and castor oil does not.

What is the fastest way to stimulate hairline regrowth?

There's no shortcut around the biology. The fastest legitimate approach combines removing the cause (usually tension or inflammation), consistent scalp massage, and a clinically supported topical like minoxidil or rosemary oil. Even with all of that in place, four to six months before visible change is realistic. Anyone promising results faster than that is probably selling you something.

Is rosemary oil as effective as minoxidil for the hairline?

One randomized controlled trial published in Skinmed in 2015 found rosemary oil and 2% minoxidil produced comparable hair-count increases in 100 patients with androgenetic alopecia at six months. Rosemary caused significantly less scalp itching. That's one study, not a body of literature, so the comparison is encouraging but not settled. Minoxidil has decades of trial data; rosemary has one good RCT.

Can traction alopecia hairline loss grow back?

Early-stage traction alopecia, where follicles are stressed but not yet scarred, is generally reversible once the tension comes off. The AAD notes that prompt discontinuation of the offending hairstyle is the first and most effective treatment. Late-stage traction alopecia with follicular fibrosis is not reversible with topical treatment. A dermatologist can stage your alopecia so you know which category you're in.

How many times a week should I massage my hairline for hair growth?

The most-cited scalp massage study used a daily protocol of four minutes per session for 24 weeks, which produced measurable increases in hair thickness. Daily is the evidence-based frequency, but five days a week is likely still helpful. The variables that matter are consistency and technique: fingertip pads, small circular motions, moderate pressure, no nail scratching. Doing it well four days a week beats doing it sloppily every day.

Does minoxidil work on the hairline specifically?

Minoxidil is FDA-approved for scalp hair loss broadly, but most trials focused on the crown and vertex, not the frontal hairline. Dermatologists use it at the hairline off-label, and the reasoning holds up since the mechanism (extending anagen and increasing follicle size) applies across the scalp. Results may be more modest at the hairline than at the crown. Ask a board-certified dermatologist about application and whether 2% or 5% suits you.

What vitamin deficiency causes hairline thinning?

Low ferritin (stored iron) is the most consistently documented nutritional contributor to hair loss in women, tied to chronic telogen effluvium in multiple studies. Vitamin D deficiency has also been linked to alopecia in observational research. Zinc and B12 deficiency can also cause shedding. The right order is bloodwork first, supplementation second. Don't take iron without a confirmed deficiency, because excess iron causes its own problems.

Can I stimulate dormant hairline follicles with essential oils?

Rosemary oil is the best-supported essential oil for hairline stimulation, backed by one head-to-head RCT against minoxidil. Peppermint oil has promising but preliminary data. Oils like tea tree and lavender help scalp health but have no strong hair regrowth evidence. Essential oils must always be diluted in a carrier oil before touching skin; standard dilution for scalp use is 1 to 2%, about 2 to 3 drops per teaspoon of carrier oil.

What protective styles are safe for thinning edges?

Any style that keeps hair tucked away without pulling the hairline qualifies. Box braids with no extensions at the perimeter, loose twists, low-tension wigs on a wig grip (no adhesive), and satin-lined caps are all good options. The test is simple: if you feel any pull or tension at the hairline during install or wear, the style is too tight for a recovering edge. See our guide to protective hairstyles for specifics.

How long does it take for baby hairs to grow back at the hairline?

If the follicles are still alive, new baby hairs usually become visible within three to five months of removing the cause and starting a supportive routine. Those first hairs will be very fine and short. It takes another three to six months for them to grow enough length and thickness to see clearly. Full recovery of edge density, if it happens, usually takes twelve to eighteen months of consistent care.

Can postpartum hair loss cause permanent edge thinning?

Postpartum hair loss (telogen effluvium triggered by the hormonal drop after delivery) is almost always temporary. Most people see shedding peak around three to four months postpartum, with regrowth beginning by six to nine months. The hairline often thins most visibly because those follicles are the finest. Edges lost to postpartum shedding usually return on their own, but if you also have tight styling habits, the combination can turn persistent.

Is PRP worth it for hairline regrowth?

PRP (platelet-rich plasma) has decent evidence for hair density improvement in androgenetic alopecia, with a 2019 meta-analysis in Dermatologic Surgery finding statistically significant improvements across multiple studies. It's expensive (typically $1,500 to $3,000 for a course), not covered by insurance, and results vary. It's a reasonable option if non-invasive treatments have run consistently for six months without result, and a dermatologist has confirmed the follicles are still viable.

Sources

1. NIH National Library of Medicine, StatPearls: Hair Follicle Anatomy: Hair follicles cycle through anagen, catagen, and telogen phases; follicles in extended telogen are dormant but not necessarily permanently lost
2. American Academy of Dermatology, Hair Loss Types: AAD identifies traction alopecia as a leading cause of hairline loss in African American women and states early-stage loss is reversible with prompt style changes
3. NIH National Library of Medicine, StatPearls: Telogen Effluvium: Postpartum estrogen drop pushes follicles into telogen en masse, typically producing peak shedding three to four months after delivery
4. NIH National Library of Medicine, StatPearls: Androgenetic Alopecia: Androgenetic alopecia affects roughly 50% of women by age 50 through progressive follicle miniaturization
5. Journal of the American Academy of Dermatology: Low serum ferritin is associated with chronic telogen effluvium; vitamin D and zinc deficiency are also linked to hair loss in women
6. Journal of the American Academy of Dermatology, Traction Alopecia Review 2019: Patients who discontinued the offending hairstyle in early-stage traction alopecia showed significant regrowth; late-stage patients with follicular scarring did not respond to treatment
7. FDA, Drugs Section: Minoxidil Approval: Minoxidil 2% is the FDA-approved topical for female pattern hair loss; 5% foam is used off-label with clinical evidence; efficacy is limited in fully fibrosed follicles
8. Skinmed, Rosemary Oil vs. Minoxidil RCT (Panahi et al., 2015): Rosemary oil produced comparable hair count increases to 2% minoxidil in 100 androgenetic alopecia patients at 6 months, with significantly less scalp itching
9. ePlasty, Standardized Scalp Massage Study (Koyama et al., 2016): Four minutes of daily standardized scalp massage for 24 weeks produced significant increases in hair thickness in nine male participants
10. International Journal of Dermatology, Topical Caffeine and Hair Follicle Study: Topical caffeine penetrates the scalp and may counteract DHT-related effects at the hair follicle
11. NIH National Center for Complementary and Integrative Health: Undiluted essential oils applied to skin can cause contact dermatitis and irritation; dilution in a carrier oil is recommended
12. NIH National Institute of Arthritis and Musculoskeletal and Skin Diseases: NIAMS describes traction alopecia as gradual hair loss from pulling force and notes early diagnosis with hairstyle change often allows natural regrowth
13. International Journal of Trichology, Microneedling with Minoxidil RCT (Dhurat et al., 2013): Patients combining microneedling with minoxidil had significantly better hair count responses than those using minoxidil alone in a small randomized controlled trial
14. American Journal of Clinical Dermatology, LLLT RCT 2014: A randomized trial found significant improvement in hair density with a 9-beam low-level laser device compared to a sham device in androgenetic alopecia patients
15. NIH Office of Dietary Supplements, Vitamin D Fact Sheet for Health Professionals: NIH defines vitamin D deficiency as serum 25-hydroxyvitamin D below 20 ng/mL