Can applying a mask with PP405 directly to thinning areas give your scalp the push it needs?

Hair loss affects millions of people and is often accompanied by a question as simple as it is hopeful: if I apply a product with PP405 right where I have less hair, can it grow back? The short answer is that the question rests on a mistake — no product containing PP405 is on sale, and PP405 does not do what the mask marketing suggests.

This article sets out what PP405 actually is, what the published research says, and why a mask is the wrong format for the job in any case.

What is PP405 and why is it drawing attention?

PP405 is often described online as an anti-DHT ingredient. That is wrong. PP405 is an experimental topical gel from Pelage Pharmaceuticals containing a small molecule that inhibits the mitochondrial pyruvate carrier (MPC) — a transporter that controls how a cell fuels itself. It does not block DHT, does not inhibit 5-alpha reductase, and is not an antiandrogen of any kind.

The rationale comes from University of California, Los Angeles work on follicle metabolism: a 2017 paper in Nature Cell Biology reported that hair follicle stem cells depend on glycolysis and lactate production, and that pushing their metabolism in that direction activated dormant follicle stem cells in mice (Flores et al., 2017). Blocking the MPC is a way to force that shift. The 2017 paper did not test PP405 itself.

PP405 has not been approved by the FDA or any other regulator, and it is not present in any cosmetic or pharmaceutical product on the market. Anything sold as a "PP405 mask", serum or shampoo is not the trial compound.

What does "loss of hair density" mean and why does it matter?

Talking about loss of hair density means a decrease in the number of hairs per square centimeter on the scalp.

It doesn't necessarily imply total baldness but rather a progressive thinning of hair volume that can worsen over time. Hair density is determined by the balance between natural hair shedding and its growth cycle, which includes the anagen (growth), catagen (transition), and telogen (resting) phases.

In pattern hair loss, the standard description is that the anagen phase gets progressively shorter while a larger share of follicles sit in telogen, so the scalp carries fewer growing hairs at any one time and the hairs that do grow are finer and shorter. That is a description of the process, not a measurement from any single study.

What causes hair density loss?

There are many causes of density loss, but one of the main ones is androgenetic alopecia. In this type of hair loss, the enzyme 5-alpha reductase converts testosterone into dihydrotestosterone (DHT), a hormone that shortens the hair growth phase and miniaturizes follicles in genetically susceptible people.

Inhibiting that enzyme is the mechanism of the prescription drugs finasteride and dutasteride, which reduce DHT production. PP405 does not work this way and should not be grouped with them.

Another factor discussed in density loss is oxidative stress, a process in which cells produce more free radicals than the body can neutralize. A 2015 study in the Journal of Investigative Dermatology compared dermal papilla cells taken from balding and non-balding scalp in men with androgenetic alopecia; the authors reported that the balding-scalp cells showed markers of oxidative-stress-associated senescence and were more sensitive to oxidative stress in culture (Upton et al., 2015). It is laboratory work on cultured cells, and the authors present it as a mechanism to investigate rather than a reason to take antioxidants.

So, would a mask with PP405 be useful?

Set aside for a moment that no such product legitimately exists. Even for a real active ingredient, a topical has to cross several barriers to reach the follicle: the stratum corneum, the sebaceous glands, and the follicular canal. Hair masks are formulated to coat and condition the hair fiber, and are rinsed out after a few minutes — they are not a delivery system for a drug that has to reach the follicle root.

The drugs that do work topically on the scalp are formulated as solutions, foams or gels that stay on the skin — minoxidil is the familiar example, and the PP405 trials themselves used a leave-on gel, not a wash-off product. A mask can improve how hair looks and feels. It is not a route to the follicle.

What does research say about PP405 so far?

The record is short and it is all early-stage.

The preclinical basis is the 2017 mouse work on follicle stem cell metabolism described above. It is mouse work on stem cells, not a hair-loss treatment trial, and mouse hair cycling differs substantially from human hair cycling.

The clinical work on record is a registered Phase 2 trial, NCT06393452, sponsored by Pelage Pharmaceuticals. It enrolled 78 adults with androgenetic alopecia, who applied a 0.05% PP405 topical gel or a matching vehicle gel once daily. Part 1 was a randomized, quadruple-masked 28-day period; Part 2 was an open-label extension of about three months. Its listed primary outcomes were treatment-related adverse events and local skin tolerability — safety, not regrowth. The registry lists it as completed in October 2025.

There is no peer-reviewed human evidence that PP405 grows hair. Pelage has reported a subgroup hair-density result in a press release (June 2025: at week 8, 31% of men with more advanced hair loss on PP405 had a more than 20% rise in hair density, compared with 0% on placebo); it was not a registered outcome of the trial and has not been peer-reviewed. A 24-week Phase 2/3 efficacy trial in about 600 men (NCT07819435, first posted 15 September 2026), also using a leave-on gel, is listed as not yet recruiting. There is no published study of PP405 in keratinocytes, no reported effect on 5-alpha reductase, and no published in-vitro DHT work on it at all.

RU58841 is sometimes mentioned in the same breath. RU58841 is an unapproved research chemical: it is a topical antiandrogen that has never completed human trials, is not a medicine, is sold only through unregulated suppliers, and has no established safety profile. Some community members use it; that does not make it an evaluated treatment, and comparing it with PP405 tells you nothing about either.

Conclusion: Could a mask with PP405 give your scalp a boost?

On the published evidence, no. There is no approved or marketed PP405 product, no peer-reviewed human efficacy result for the compound, and no mechanism by which it would act on DHT, which is what the mask claims usually promise. The mask format is also the wrong delivery route for any follicle-targeting active.

If PP405 is ever shown to be effective and safe, it will be as a leave-on topical of the kind used in its trials, not as a rinse-out mask. Until then, masks remain useful for shine, hydration and softness — not for stopping hair loss or restoring density.

Talk to a doctor, dermatologist or pharmacist before starting, stopping or combining any hair-loss treatment, and before using any unapproved research chemical such as RU58841.

References

Flores, A., Schell, J., Krall, A. S., Jelinek, D., Miranda, M., et al. (2017). Lactate dehydrogenase activity drives hair follicle stem cell activation. Nature Cell Biology, 19(9), 1017–1026. https://pubmed.ncbi.nlm.nih.gov/28812580/

ClinicalTrials.gov. Safety, Pharmacokinetics and Efficacy of PP405 in Adults With AGA. NCT06393452. https://clinicaltrials.gov/study/NCT06393452

ClinicalTrials.gov. Phase 2/3 Efficacy and Safety of PP405 in Adult Males. NCT07819435. https://clinicaltrials.gov/study/NCT07819435

Pelage Pharmaceuticals. (17 June 2025). Pelage Pharmaceuticals Announces Positive Phase 2a Clinical Trial Results for PP405 in Regenerative Hair Loss Therapy [press release; not peer-reviewed]. https://pelagepharma.com/press-releases/pelage-pharmaceuticals-announces-positive-phase-2a-clinical-trial-results-for-pp405-in-regenerative-hair-loss-therapy/

Upton, J. H., Hannen, R. F., Bahta, A. W., Farjo, N., Farjo, B., & Philpott, M. P. (2015). Oxidative stress-associated senescence in dermal papilla cells of men with androgenetic alopecia. Journal of Investigative Dermatology, 135(5), 1244–1252. https://pubmed.ncbi.nlm.nih.gov/25647436/