Do Hair Growth Shampoos Work? Caffeine, Ketoconazole, and What a Shampoo Can Realistically Do

By Dr. Susan Lin, MD | MD HAIR | La Cañada Ventures, Inc.

You have been standing in the shampoo aisle — or scrolling a product page at 11 p.m. — reading the same promises over and over. Thickening. Regrowth. Anti-hair-loss. Clinically proven. One bottle has caffeine. Another has biotin. A third costs sixty dollars and comes with a graph on the back. And somewhere underneath the marketing you are asking the only question that actually matters: if I switch shampoos, will I stop losing hair?

I want to answer that honestly, because the honest answer is more useful than the optimistic one — and because I think the way shampoo is sold in this category has done real damage to people’s trust.

Here is the short version, and then I will show you the science behind it: a shampoo cannot be your hair loss treatment, but the right shampoo makes every other treatment work better. That sounds like a hedge. It is not. It is a description of a specific physical constraint that almost no one selling you a “hair growth shampoo” will mention.

As a physician who has spent nearly two decades formulating for hair — and who has, yes, formulated a shampoo — I would rather tell you what a shampoo genuinely does than sell you a fantasy you will abandon in eight weeks.

The Constraint Nobody Mentions: Contact Time

Start here, because everything else follows from it.

An active ingredient works on skin the way a drug works anywhere in the body: it has to reach the target tissue, at a sufficient concentration, for a sufficient duration. Dermatology has a shorthand for that third variable — contact time.

Now think about how you actually use shampoo. You wet your hair, emulsify a small amount across the scalp, massage for — realistically — thirty to ninety seconds, then rinse it deliberately and thoroughly down the drain, because that is the entire point of a surfactant product. Total scalp contact time is roughly 60 to 120 seconds, once a day at most, and for many people two or three times a week. Compare that to a leave-on serum applied to the part line, which stays on the scalp for twelve to twenty-four hours. Over a week that is two or three orders of magnitude of difference in exposure. It is not a close call.

There is a second problem stacked on the first: a shampoo is engineered to be removed. Surfactants exist to lift oil and residue off the scalp and suspend them in water so they rinse away — and any active dissolved in that same system is largely subject to the same fate. You are asking a molecule to deposit and penetrate inside a formulation whose defining function is to not leave anything behind.

This is why I ask patients a reframing question: not “does this shampoo contain a good active?” but “does this shampoo deliver a meaningful dose of that active for a meaningful duration?” For nearly every marketed hair growth shampoo, the honest answer to the second question is no — regardless of how good the ingredient is in a laboratory.

Caffeine: Real Follicular Science, Overstated Shampoo Claims

Caffeine is the most heavily marketed hair shampoo active in the world, and — this is the frustrating part — the underlying science is genuinely interesting.

What the laboratory research actually shows

In isolated human hair follicle organ culture, caffeine has been studied in the lab for its effect on follicle growth. Fischer and colleagues reported that testosterone suppressed hair shaft elongation in cultured male follicles, and that caffeine counteracted that suppression, with caffeine alone producing significant stimulation of shaft elongation (Fischer et al., 2007). A larger 2014 follow-up in the British Journal of Dermatology examined caffeine’s effects on hair matrix and outer root sheath keratinocyte proliferation and on TGF-β2 and IGF-1 signaling in both male and female follicles, again in vitro (Fischer et al., 2014).

Mechanistically, caffeine is a phosphodiesterase inhibitor — it raises intracellular cyclic AMP, which is associated with increased cell proliferation and metabolic activity. It also appears to modulate TGF-β2, a catagen-promoting signal. Those are plausible, biologically coherent mechanisms.

But note carefully what these studies are: isolated follicles, in a dish, bathed continuously in a known caffeine concentration. That is the opposite of a 90-second rinse.

The penetration study everyone cites — and what it really found

The study invoked in nearly every caffeine shampoo advertisement is Otberg and colleagues’ work on follicular penetration of topically applied caffeine delivered in a shampoo formulation (Otberg et al., 2007). It is a genuinely elegant piece of research, and it demonstrated something important: the hair follicle is a real penetration pathway. Caffeine applied to the scalp was detectable systemically, and the follicular route contributed meaningfully to absorption — with detectable levels appearing faster when follicles were open than when they were blocked.

What that study established is that the follicular infundibulum acts as a reservoir and a shunt into deeper tissue. That is a legitimate and useful finding — related work has characterized hair follicles as an efficient storage and penetration route for topically applied substances (Lademann et al., 2008), and follicle density and size vary substantially by body site, which affects how much of this pathway is available (Otberg et al., 2004).

What that study did not establish is that caffeine shampoo regrows hair. It measured penetration, not clinical outcome. A molecule getting into the follicular canal is a necessary condition for efficacy — not a demonstration of it. Somewhere between the journal and the bottle, “caffeine can penetrate via the follicle” became “caffeine shampoo reverses hair loss.” Those are not the same sentence.

My honest read

Caffeine is a legitimate ingredient with real laboratory support and an excellent safety profile. In a leave-on vehicle, where contact time is measured in hours, the argument for it is far stronger. In a rinse-off shampoo, I regard it as a reasonable and pleasant inclusion — not a treatment. If a shampoo’s entire value proposition is its caffeine content, you are buying a study that was never about shampoo efficacy.

Ketoconazole 2%: The Strongest Evidence in the Category — With Caveats

If any shampoo active has earned a serious hearing, it is ketoconazole.

Ketoconazole is an antifungal, used at 2% (prescription) and 1% (over the counter) primarily against Malassezia-driven seborrheic dermatitis and dandruff. Its relevance to hair loss emerged from two observations. First, it suppresses the yeast overgrowth that drives scalp inflammation — and perifollicular inflammation is a recognized co-factor in the miniaturization process. Second, ketoconazole appears to have intrinsic anti-androgenic activity at the local level.

The most cited clinical work here is Piérard-Franchimont and colleagues, who reported that long-term use of 2% ketoconazole shampoo produced improvements in hair density and pilary index in men with androgenetic alopecia, with effects described as comparable in magnitude to a 2% minoxidil comparator arm (Piérard-Franchimont et al., 1998). Inui and Itami later argued that topical ketoconazole’s benefit in pattern hair loss reflects genuine local anti-androgenic activity rather than antifungal action alone (Inui & Itami, 2007). Separately, a randomized controlled trial found that 1% pyrithione zinc shampoo produced a modest but statistically significant increase in hair count versus placebo, though less than 5% minoxidil (Berger et al., 2003) — reinforcing that anti-inflammatory, anti-Malassezia scalp control has a measurable, if modest, effect.

So the category is not fraudulent. Something real is happening.

But read the caveats with equal care. The foundational trials are small, with sample sizes and designs that would not clear the bar of a modern pivotal study. The effect size is modest — a supporting contribution, not a primary therapy. The mechanism is largely inflammatory control, which means the benefit is greatest in people whose scalps are genuinely inflamed; if you do not have seborrheic dermatitis, you have less to gain. And ketoconazole is a drug: at 2% it is prescription in the United States, and long-term daily antifungal use is a decision to make with your own physician — not something to start on your own based on a blog post, including this one.

The ketoconazole literature is, to me, the clearest proof of this article’s thesis: the measurable benefit of a medicated shampoo comes from fixing the scalp environment, not from dosing the follicle.

What a Shampoo Genuinely Can Do

Now the constructive half. A shampoo is not a treatment — but it is not decoration either. Here is what it does that nothing else in your routine can:

1. It removes sebum and the androgens carried in it

Sebaceous glands are androgen-responsive tissue, and the pilosebaceous unit expresses 5α-reductase locally, generating DHT within the skin itself rather than importing all of it from circulation (Chen et al., 1996). Sebum sitting on the scalp is therefore not inert grease — it is a lipid layer in intimate contact with the follicular opening, carrying androgenic and inflammatory signaling molecules with it. Regular, effective cleansing physically reduces that load. This is the least glamorous and most underrated function of a shampoo.

2. It clears the follicular infundibulum

The Otberg and Lademann line of research makes the point implicitly: the follicular opening is a delivery route. A canal packed with oxidized sebum, styling polymers, silicone residue, and corneocyte debris is a blocked delivery route. Cleansing keeps the pathway patent. This is precisely why shampoo belongs before your serum, not instead of it.

3. It reduces Malassezia load and perifollicular inflammation

This is where the medicated-shampoo evidence sits. A calmer scalp is a better environment for follicles — less itching, less scratching, less chronic low-grade inflammatory signaling around the bulb.

4. It reduces mechanical breakage — which is not regrowth, but looks like it

Harsh surfactants strip the lipid layer of the cuticle, raise the scales, and leave the shaft rough, high-friction, and prone to snapping mid-length. Someone with cosmetic breakage often reports “hair falling out” when the shaft is fracturing, not shedding from the root. Gentler surfactant systems and a properly conditioning follow-up reduce that fracture rate. Retained length is not new growth — but it is retained density, and it is visible.

5. It prepares the scalp for the products that actually treat

This is the real job. A clean, non-occluded, non-inflamed, well-buffered scalp is the substrate on which a leave-on active performs. In a 119-day (17-week) open-label study conducted by Spincontrol North America on MD’s two-step leave-on topical serum system (n=24, no placebo arm, outcomes self-reported by questionnaire), 71% of participants agreed their hair growth had improved — and the report itself cautions that the overall satisfaction rate was “not significantly validated.” Individual results vary. The point of citing it here: that study was conducted on leave-on topicals — and leave-on topicals are applied to a scalp that a shampoo prepared.

Sulfate-Free: Useful Nuance, Not a Moral Category

“Sulfate-free” has become a shorthand for virtue, which is a shame, because the actual argument is more interesting than the slogan.

Sodium lauryl sulfate is a highly effective, aggressive anionic surfactant. It cleans exceptionally well and, in sensitive individuals, is a well-recognized irritant — which is exactly why dermatology research has historically used SLS as a standard positive control for inducing irritant contact dermatitis in patch testing. That is a striking fact about a molecule sold for daily scalp use.

The nuance: sulfates are not toxic and do not cause hair loss. But for a compromised, inflamed, or already thinning scalp, aggressive delipidation is counterproductive — you want the barrier intact — and milder amphoteric and non-ionic surfactant systems clean adequately for most people with far less disruption. “Sulfate-free” also tells you nothing on its own about whether the rest of the formula is good.

My clinical position: for someone actively managing hair loss, a gentler surfactant system is the sensible default, because the scalp barrier is part of the treatment surface. That is a formulation judgment, not a purity ideology.

Peptides deserve the same honest framing. Signal peptides such as Biotinoyl Tripeptide-1 have been studied in the lab for their interaction with follicular tissue. That research is real — and it is research on sustained exposure. A peptide in a rinse-off product is subject to precisely the contact-time constraint we started with. Peptides belong in your leave-on step. A shampoo containing them is a nice bonus, not the reason to buy it.

The Honest Verdict

A shampoo is the foundation. It is not the treatment.

A foundation is not optional — build a treatment regimen on an inflamed, occluded, mechanically damaged scalp and you will underperform. But you cannot live in a foundation either. Expecting regrowth from a rinse-off product is expecting a 90-second exposure to accomplish what a 12-hour exposure is designed to do.

Practically: buy a shampoo for what a shampoo does — cleansing quality, surfactant gentleness, scalp comfort, breakage reduction, barrier preservation. Do not pay a premium for a rinse-off active you would get far more from in a leave-on form. Judge it on scalp feel and breakage over four to eight weeks, not on regrowth, because regrowth is not its job. Layer correctly: cleanse, then treat, with the serum going onto a clean scalp. And if your scalp is genuinely flaking, red, or itching, talk to your physician about a medicated shampoo — that is where the strongest shampoo evidence lives, and it is a medical decision.

If a bottle promises regrowth in four weeks, you have learned something valuable about the company, just not about your hair.

The Bottom Line

Caffeine has real laboratory support at the follicle and a legitimate follicular penetration pathway — but the penetration research was never a regrowth trial, and a rinse-off vehicle cannot deliver the sustained exposure the laboratory work relied on. Ketoconazole 2% has the strongest clinical evidence in the shampoo category, and its benefit appears to come mainly from controlling Malassezia and perifollicular inflammation — real, modest, and a prescription decision for your own doctor.

A shampoo’s honest contribution is to remove sebum and the androgens it carries, clear the follicular opening, calm inflammation, reduce mechanical breakage, and hand a clean, intact scalp to the products that actually treat. That is a genuinely valuable job. It is simply not the same job as regrowth.

Choose your shampoo well, expect the right things from it, and put your regrowth expectations where the contact time is.

Dr. Susan Lin’s Clinical Perspective

“When a patient tells me they have tried six hair growth shampoos and nothing worked, my honest reaction is that the shampoos were never the variable. The category’s failure is not bad ingredients — caffeine, ketoconazole, and peptides all have real literature behind them. The failure is pharmacokinetic: you cannot dose a follicle in ninety seconds with a product engineered to rinse away. What I actually want from a cleanser is a gentle surfactant system that lifts sebum-bound androgens and debris out of the follicular infundibulum, calms the scalp instead of stripping it, and leaves the cuticle intact so length is not lost to breakage. Do that consistently and you have built the surface every leave-on active depends on. The mistake I see most often is people spending their entire budget on the rinse-off step and nothing on the step that stays. Cleanse to prepare. Treat with what remains.”

— Dr. Susan Lin, MD, Physician Formulator, MD HAIR

Mechanism Spotlight: The Follicular Infundibulum as Reservoir — and Why Rinse-Off Wastes It

The upper segment of the hair follicle — the infundibulum, the funnel between the skin surface and the sebaceous duct — is one of the most important structures in topical scalp science. Otberg and colleagues showed that hair follicles vary substantially in size, density, and volume across body sites, meaning the available follicular reservoir differs from scalp to forearm (Otberg et al., 2004). Subsequent work characterized these openings as an efficient storage and penetration route for topically applied substances, with material deposited in the canal releasing into surrounding tissue over an extended period — a slow-release depot formed by the skin itself (Lademann et al., 2008). The caffeine-via-shampoo penetration study exploited exactly this pathway, demonstrating that follicular delivery meaningfully accelerated systemic appearance of caffeine compared with blocked follicles (Otberg et al., 2007). Here is the clinical irony. This reservoir is a genuine advantage for topical scalp therapy — and a rinse-off product squanders it twice over: the exposure window is too brief to load the depot, and the surfactant system actively strips deposited material from the canal on its way out. The same anatomy that makes leave-on scalp actives worth applying is the anatomy that makes shampoo a poor delivery vehicle. Cleansing keeps the reservoir open. Something else has to fill it.

Recommended Reading

Pillar pages on mdhair.com:

Related articles in this series:

Not sure where your hair loss fits? Take the MD HAIR Quiz.

For our broader physician-formulated line and the original MD® formulations, our established sister site md-factor.com remains the deeper archive on the MD® platform.

MD HAIR Product Recommendation

MD® Shampoo & Conditioner Bundle

I formulated the MD® shampoo and conditioner to do the foundation job properly and to be honest about what that job is. The shampoo uses a gentle, sulfate-free surfactant system chosen to lift sebum, styling residue, and debris out of the follicular infundibulum without stripping the scalp barrier — because an inflamed, delipidated scalp is a poor surface for anything you apply afterward. The conditioner is the half people skip and should not: smoothing the cuticle reduces friction and mid-shaft fracture, and retained length reads as density in the mirror even before any new growth appears. Both are drug-free and hormone-free. I recommend the bundle rather than either piece alone, because cleansing and cuticle repair are one process. Use it as step one — then apply your leave-on treatment to the clean scalp it prepares. And if the caffeine science is what brought you here, note where caffeine belongs on the logic of this article: in the leave-on step. MD® Scalp Essential is the leave-in scalp serum in our line that carries caffeine — alongside mandelic acid and lilac stem-cell extract with CLA glutathione — with the contact time a rinse-off product cannot offer. Physician-formulated by Dr. Susan F. Lin, M.D., and made in FDA-registered, GMP-compliant facilities in the USA.

Genuine MD HAIR and MD Nutri Hair™ products are sold only through mdhair.com, md-factor.com, and the official La Cañada Ventures, Inc. stores on Amazon and Walmart.

References

  1. Fischer TW, Hipler UC, Elsner P. (2007). Effect of caffeine and testosterone on the proliferation of human hair follicles in vitro. International Journal of Dermatology, 46(1), 27–35. PubMed
  2. Fischer TW, et al. (2014). Differential effects of caffeine on hair shaft elongation, matrix and outer root sheath keratinocyte proliferation, and TGF-β2/IGF-1-mediated regulation of the hair cycle in male and female human hair follicles in vitro. British Journal of Dermatology, 171(5), 1031–1043. PubMed
  3. Otberg N, et al. (2007). Follicular penetration of topically applied caffeine via a shampoo formulation. Skin Pharmacology and Physiology, 20(4), 195–198. PubMed
  4. Otberg N, et al. (2004). Variations of hair follicle size and distribution in different body sites. Journal of Investigative Dermatology, 122(1), 14–19. PubMed
  5. Lademann J, et al. (2008). Hair follicles — an efficient storage and penetration pathway for topically applied substances. Skin Pharmacology and Physiology, 21(3), 150–155. PubMed
  6. Piérard-Franchimont C, De Doncker P, Cauwenbergh G, Piérard GE. (1998). Ketoconazole shampoo: effect of long-term use in androgenic alopecia. Dermatology, 196(4), 474–477. PubMed
  7. Inui S, Itami S. (2007). Reversal of androgenetic alopecia by topical ketoconazole: relevance of anti-androgenic activity. Journal of Dermatological Science, 45(1), 66–68. PubMed
  8. Berger RS, et al. (2003). The effects of minoxidil, 1% pyrithione zinc and a combination of both on hair density: a randomized controlled trial. British Journal of Dermatology, 149(2), 354–362. PubMed
  9. Chen W, Zouboulis CC, Orfanos CE. (1996). The 5α-reductase system and its inhibitors: recent development and its perspective in treating androgen-dependent skin disorders. Dermatology, 193(3), 177–184. PubMed

Dr. Susan F. Lin, M.D. is the physician formulator behind MD HAIR, a line of drug-free, clinically informed hair products by La Cañada Ventures, Inc. — physician-formulated since 2008, under the MD® mark. MD HAIR topical products are cosmetics; they are not intended to diagnose, treat, cure, or prevent any disease. MD Nutri Hair™ is a dietary supplement. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Manufactured in FDA-registered, GMP-compliant facilities in the USA; facility registration is not product approval by the FDA. This article is for educational purposes and does not constitute medical advice. Do not start, stop, or change any medication — including prescription medicated shampoos — without consulting your own physician. Because there are no clinical data in pregnant or breastfeeding women, we do not advocate using MD HAIR products during pregnancy or lactation.