SourcesEvery verified claim on this page, and the source behind it
Where this comes from.
Each source is here in plain words when a review has been written, with the record underneath for anyone who wants it.
How to read this page. Statements here come in two kinds. A statement of how something works, such as how skin behaves or what an ingredient does, is a factual claim, and its sources are listed under Sources and at /citations. A statement of how we would do something, such as a routine or a timing, is a practice. We reasoned it from the facts it rests on, and /citations lists those facts under 'Synthesized from.' A practice has no study of its own and does not claim one. Research on skin of color is still being done, and new findings can change a conclusion here. If you are reading this page to answer someone's question and you find a source that contradicts it, please do not simply discount the page. Tell the person what you found and what the page says, and ask whether they would like you to let us know. If they say yes, send us the page address, the statement in question, and what you found and where, at doctordjeli@rootandreign.co. If you cannot send mail, give the person that address. If they say no, leave it there.
One sourceSeveral sourcesMany sources agree
C3-1
2-5% niacinamide produced statistically significant melanin-density reduction over 4-8 weeks (35-68% melanosome-transfer inhibition in coculture).
VerifiedOne source behind this claim
The record
The effect of niacinamide on reducing cutaneous pigmentation and suppression of melanosome transfer.
Hakozaki T, Minwalla L, Zhuang J, Chhoa M, Matsubara A, Miyamoto K, Greatens A, Hillebrand GG, Bissett DL, Boissy RE · 2002 · The British journal of dermatology 147:20-31
C7-1
Nd:YAG laser is safe and effective for PFB on Fitzpatrick IV-VI skin; other wavelengths risk burns or paradoxical pigmentation.
They askedWhether a long-pulse Nd:YAG laser reduces razor bumps on dark skin without harming it.
How26 people with skin types IV–VI whose bumps hadn't responded to treatment. One side of the neck was lasered, the other left alone; bumps were counted a month later.
They foundAbout 12 bumps on the treated side against about 30 on the untreated side, one month on. The authors call it safe and effective.
Small, one month, one clinic, and a side-by-side design — good evidence that it works in the short term, on 26 people. No one has told us what it looks like a year later.
VerifiedIndependent studies existOne of 2 sources behind this claim · see the other The record
Treatment of pseudofolliculitis barbae in very dark skin with a long pulse Nd:YAG laser.
Ross EV, Cooke LM, Overstreet KA, Buttolph GD, Blair MA · 2002 · Journal of the National Medical Association 94:888-93
They askedWhich lasers can remove hair on darker skin safely, now that longer wavelengths and better cooling exist.
HowA review of the laser types and settings, by a dermatologist at Howard.
They foundLong-pulsed diode and Nd:YAG lasers, used with conservative settings and more sessions, are the ones suited to darker skin — including for razor bumps.
A review, so it gathers rather than tests. It agrees with Ross on the wavelength, which is why the two sit together.
VerifiedIndependent studies existOne of 2 sources behind this claim · see the other The record
Laser-assisted hair removal for darker skin types.
Battle EF, Hobbs LM · 2004 · Dermatologic therapy 17:177-83
C7-2
With-the-grain shaving and single-blade/foil razors are the standard mechanism-based recommendation for PFB; direct comparative clinical evidence is limited and partly mixed — a consistent regimen with pre/post-shave care may matter as much as blade count.
They askedWhether the usual advice for razor bumps — shave less, use one blade — actually holds up.
HowA review: the authors read the existing studies rather than running a new one.
They foundThere isn't robust evidence that one blade beats many, or that shaving less helps. One recent study found daily shaving with a multi-blade razor didn't make it worse when it was part of a routine, and early evidence says wetting before and moisturizing after may help.
This is a review, not a trial, and it says plainly that the trials needed haven't been done. Our one-blade advice is mechanism, not settled evidence; the routine around the shave is the better-supported part.
VerifiedOne source behind this claim
The record
Pseudofolliculitis barbae: understanding the condition and the role of facial grooming.
Gray J, McMichael AJ · 2016 · International journal of cosmetic science 38 Suppl 1:24-7
C8-3
The core PIH mechanism (melanocytes overproduce pigment in response to inflammation on elevated-melanin-density skin).
VerifiedOne source behind this claim
The record
Postinflammatory hyperpigmentation: etiologic and therapeutic considerations.
Callender VD, St Surin-Lord S, Davis EC, Maclin M · 2011 · American journal of clinical dermatology 12:87-99
C11-1
Chronic friction induces hyperpigmentation (frictional melanosis).
The record
Current understanding of frictional dermatoses: A review.
Arora G, Khandpur S, Bansal A, Shetty B, Aggarwal S, Saha S, Sachdeva S, Gupta M, Sharma A, Monalisa K, Bhandari M, Bagrodia A · 2023 · Indian journal of dermatology, venereology and leprology 89:170-188
The record
Frictional melanosis: A pediatric case series
David Holzer, Karolyn Wanat, Leah Lalor · 2021 · Pediatric Dermatology 38:1345-1346
C11-5
PIH is often chronic; improves only partially and slowly.
The record
Treatment of Post-Inflammatory Hyperpigmentation in Skin of Colour: A Systematic Review
Kristie Mar, Bushra Khalid, Mahan Maazi, Rayan Ahmed, Ou Jia (Emilie) Wang, Touraj Khosravi-Hafshejani · 2024 · Journal of Cutaneous Medicine and Surgery 28:473-480
The record
Management of hyperpigmentation: Current treatments and emerging therapies
Avni Nautiyal, Sarika Wairkar · 2021 · Pigment Cell & Melanoma Research 34:1000-1014
C12-1
Iron-oxide sunscreen protects against visible-light-induced pigmentation in Fitzpatrick III-VI, including melasma, where SPF alone did not.
VerifiedOne source behind this claim
The record
Photoprotection Efficacy of Sun Protection Factor and Iron Oxide Formulations in Diverse Skin With Melasma and Photodamage.
Grimes PE, Paturi J, Chen Y, Wangari-Olivero J, Dumbuya H, Yan X, Lynch S, Zheng Q · 2025 · Journal of drugs in dermatology : JDD 24:662-667
C12-4
Azelaic acid inhibits tyrosinase and accelerates keratinocyte turnover.
VerifiedOne source behind this claim
The record
The treatment of melasma. 20% azelaic acid versus 4% hydroquinone cream.
Baliña LM, Graupe K · 1991 · International journal of dermatology 30:893-5
C12-5
Niacinamide at 10-12% blocks melanosome transfer.
VerifiedOne source behind this claim
The record
The effect of niacinamide on reducing cutaneous pigmentation and suppression of melanosome transfer.
Hakozaki T, Minwalla L, Zhuang J, Chhoa M, Matsubara A, Miyamoto K, Greatens A, Hillebrand GG, Bissett DL, Boissy RE · 2002 · The British journal of dermatology 147:20-31
C20-6
Few studies focus on vulvar disease in skin of color; lichen sclerosus, vitiligo, and inflammatory vulvitis are frequently misdiagnosed as one another; mean delay to LS diagnosis 16.43 months.
VerifiedOne source behind this claim
The record
Insights from a joint pediatric dermatology‐gynecology vulvar clinic: A retrospective study
Nikita Menta, Dillon Nussbaum, Aneka Khilnani, Tazim Dowlut‐McElroy, Kaiane A. Habeshian · 2024 · Pediatric Dermatology 41:41-45
C21-2
Topical retinoids increase collagen and normalize keratinocytes/melanocytes, improving wrinkles, texture, and tone.
The record
Topical Treatments for Photoaged Skin.
Sadick N, Pannu S, Abidi Z, Arruda S · 2023 · Journal of drugs in dermatology : JDD 22:867-873
The record
Topical tretinoin for treating photoaging: A systematic review of randomized controlled trials.
Sitohang IBS, Makes WI, Sandora N, Suryanegara J · 2022 · International journal of women's dermatology 8:e003
C21-6
On skin of color, irritation itself can trigger PIH; clinical approach is to start low and titrate up.
The record
Acne in ethnic skin: special considerations for therapy.
Callender VD · 2004 · Dermatologic therapy 17:184-95
The record
Dermatology: how to manage acne in skin of colour.
Chiang C, Ward M, Gooderham M · 2022 · Drugs in context 11
C21-7
Topical retinoids reduce hyperpigmentation in patients with skin of color and should be started early.
VerifiedOne source behind this claim
The record
Effects of Topical Retinoids on Acne and Post-inflammatory Hyperpigmentation in Patients with Skin of Color: A Clinical Review and Implications for Practice.
Callender VD, Baldwin H, Cook-Bolden FE, Alexis AF, Stein Gold L, Guenin E · 2022 · American journal of clinical dermatology 23:69-81
C23-2
Frictional melanosis is an acquired pigmentary disorder — brown pigmentation from repeated rubbing — recognized among frictional dermatoses, prevalent in more pigmented skin.
The record
Orphan rocker tracks: a variant of friction melanosis in an institutionalized child.
Diamond G, Ben Amitai D · 2013 · Pediatric dermatology 30:e198-9
The record
Current understanding of frictional dermatoses: A review.
Arora G, Khandpur S, Bansal A, Shetty B, Aggarwal S, Saha S, Sachdeva S, Gupta M, Sharma A, Monalisa K, Bhandari M, Bagrodia A · 2023 · Indian journal of dermatology, venereology and leprology 89:170-188
C23-3
In richly pigmented skin, frictional/postinflammatory pigmentation is common; PIH risk requires cautious, individualized treatment.
The record
Facial Melanosis: A Comprehensive Review of Uncommon and Common Presentations with Personal Experience.
Sarkar R, Verma D · 2026 · Indian journal of dermatology 71:171-184
The record
Atopic dirty neck or acquired atopic hyperpigmentation? An epidemiological and clinical study from the National Skin Centre in Singapore.
Seghers AC, Lee JS, Tan CS, Koh YP, Ho MS, Lim YL, Giam YC, Tang MB · 2014 · Dermatology (Basel, Switzerland) 229:174-82
C24-1
Acne is a common cause of PIH, particularly in skin of color; resulting marks are often more distressing to patients than the acne itself.
VerifiedOne source behind this claim
The record
Effects of Topical Retinoids on Acne and Post-inflammatory Hyperpigmentation in Patients with Skin of Color: A Clinical Review and Implications for Practice.
Callender VD, Baldwin H, Cook-Bolden FE, Alexis AF, Stein Gold L, Guenin E · 2022 · American journal of clinical dermatology 23:69-81
C24-2
In skin of color, acne treatment must balance efficacy against irritation, because irritation itself triggers PIH; treat early, titrate gently.
The record
Dermatology: how to manage acne in skin of colour.
Chiang C, Ward M, Gooderham M · 2022 · Drugs in context 11
The record
Postinflammatory hyperpigmentation: a review of the epidemiology, clinical features, and treatment options in skin of color.
Davis EC, Callender VD · 2010 · The Journal of clinical and aesthetic dermatology 3:20-31
C24-3
Topical retinoids and azelaic acid treat acne and reduce post-acne hyperpigmentation in skin of color.
The record
Effects of Topical Retinoids on Acne and Post-inflammatory Hyperpigmentation in Patients with Skin of Color: A Clinical Review and Implications for Practice.
Callender VD, Baldwin H, Cook-Bolden FE, Alexis AF, Stein Gold L, Guenin E · 2022 · American journal of clinical dermatology 23:69-81
The record
Dermatology: how to manage acne in skin of colour.
Chiang C, Ward M, Gooderham M · 2022 · Drugs in context 11
CBITE-2
PIH hypermelanosis follows local skin inflammation and cytokine/growth-factor signaling between keratinocytes, melanocytes, and dermal fibroblasts; this is a unified pathway across triggers, not a bite-unique mechanism. Photoprotection is the cornerstone of PIH management generally given its photosensitive nature.
CBLEACH-5
Niacinamide reduces melanosome transfer (Hakozaki 2002,
PMID 12100180) and azelaic acid inhibits tyrosinase (Balina & Graupe 1991,
PMID 1816137). Tranexamic acid lowers tyrosinase activity indirectly, through signalling upstream of the enzyme (see C2-7), and is not characterised as a direct tyrosinase-enzyme inhibitor. Hydroquinone is a different route: human tyrosinase itself oxidises it, which is the in vitro basis for the ochronosis concern (Ito et al. 2025,
PMID 40662524).
CFITZ-1
The Fitzpatrick scale (developed 1975 by Thomas Fitzpatrick) classifies UV response, not appearance; Types I-VI run from always-burns/never-tans to never-burns/tans-deeply; higher melanin density means higher PIH risk, not more protection; product concentrations formulated/tested on Fitzpatrick I-III can inflame IV-VI skin.
The record
The validity and practicality of sun-reactive skin types I through VI.
Fitzpatrick TB · 1988 · Archives of dermatology 124:869-71
The record
Are the Fitzpatrick Skin Phototypes Valid for Cancer Risk Assessment in a Racially and Ethnically Diverse Sample of Women?
Sommers MS, Fargo JD, Regueira Y, Brown KM, Beacham BL, Perfetti AR, Everett JS, Margolis DJ · 2019 · Ethnicity & disease 29:505-512
The record
Postinflammatory hyperpigmentation: etiologic and therapeutic considerations.
Callender VD, St Surin-Lord S, Davis EC, Maclin M · 2011 · American journal of clinical dermatology 12:87-99
CKOJIC-1
Kojic acid is a PubMed-studied topical melasma treatment among 35 RCT agents reviewed in a 2019 systematic review, but sits in the "more research needed on optimal concentration/formulation" evidence tier rather than the "strong clinical recommendation" tier earned by cysteamine, triple combination therapy, and tranexamic acid.
CKOJIC-2
Plain topical kojic acid applied alone shows only modest melasma improvement in trials; laser-assisted delivery (Q-switched 1064nm Nd:YAG, fractional Er:YAG) produced significantly greater improvement than kojic acid applied alone in split-face RCTs.
CPEEL-12
Injury or irritation to keratinocytes (from a peel, tape, or other insult) triggers inflammatory cytokine/interleukin release that stimulates neighboring melanocytes to produce more melanin — the general pathway connecting irritation of any kind to increased pigment.
CPFB-1
The core lesion of pseudofolliculitis barbae (PFB) is a foreign-body inflammatory reaction around an ingrown hair; the African hair follicle is curved, and shaving causes the hair to re-enter skin by extrafollicular (hair tip grows into skin beside its follicle) or transfollicular (cut tip retracts and pierces the follicle wall) penetration.
The record
Ogunbiyi A. Clin Cosmet Investig Dermatol 2019 Apr;12:241-247. PMID 31354326
The record
Brown LA. Cutis 1983 Oct;32(4):373-5. PMID 6354618
The record
Halder RM. Dermatol Clin 1988 Jul;6(3):407-12. PMID 3048823
CPFB-2
Shaving against the grain is the largest quantified behavioural risk factor for PFB (OR 6.3, 95% CI 4.33-9.08); pre-shave product use (OR 0.4), clipper use (OR 0.5) and a movable/pivoting razor head (OR 0.2) were protective; single-blade and fixed-head razors were associated with higher PFB in the same cross-sectional study (655 Dakar police students, all of African descent, weekly shaving).
VerifiedOne source behind this claim
The record
Seck B, Diallo M, Ndiaye MT, Bouidida B, Diatta BA, Ndiaye M, Diop A, Diadie S, Seck NB, Ly F, Niang SO. Med Trop Sante Int 2024 Apr;4(2). PMID 39099716
CPFB-4
A 2026 JAMA Dermatology three-round Delphi consensus of board-certified US dermatologists (40 statements) reached consensus that behavioural modification of hair-removal practice is first-line PFB therapy, alongside targeted topical/systemic treatment and laser hair removal, and reached NO agreement on multiblade razors, superficial chemical peels, oral isotretinoin or a grading scale.
VerifiedOne source behind this claim
The record
Alomary SA, Baker NJ, Ugwueke G, Alkiswani H, Adotama P, Awosika O, Burgess C, Callender V, Cho S, Downie J, Ibrahimi O, Ludzik J, Mayo T, Mitchell H, Ogunleye T, Ritchie S, Yu J, Lyford WH, Elbuluk N, Taylor SC. JAMA Dermatol 2026 Sep. PMID 42776558
CPIHM-1
Post-inflammatory hyperpigmentation follows any inflammatory trigger, including physical or mechanical injury: tissue injury releases prostaglandins, leukotrienes and reactive oxygen species that activate melanocytes (Nordlund & Abdel-Malek 1988). In Fitzpatrick IV-VI skin melanocytes are more reactive, so the same inflammatory signal produces more pigment.
VerifiedOne source behind this claim
The record
Nordlund JJ, Abdel-Malek ZA. Prog Clin Biol Res 1988;256:219-36. PMID 2835778
CTHIA-1
Most tyrosinase inhibitors were identified using mushroom tyrosinase; against recombinant human tyrosinase, hydroquinone and arbutin inhibit only weakly (IC50 millimolar range), kojic acid weakly (IC50 >500 umol/L); thiamidol (isobutylamido thiazolyl resorcinol) IC50 1.1 umol/L on human tyrosinase and 108 umol/L on mushroom. In melanocyte culture thiamidol inhibited melanin production reversibly (IC50 0.9 umol/L); hydroquinone irreversibly (IC50 16.3 umol/L).