A clinical study designed around the hair-care habits of African American women shows that scalp care can be effective without asking consumers to change the wash routine that works for them.
For many women with textured hair, wash day is not a daily event—it is a carefully planned part of a broader hair-care routine. Protective styles, moisture needs, styling practices, and personal preferences often mean washing once per week rather than multiple times per week.
"For many women with textured hair, wash day is about more than just cleansing the scalp. We also have to consider replenishing moisture, detangling, and styling.” said Dr. Cheri Frey, Board-Certified Dermatologist. Many women use protective styles or other practices that make frequent washing impractical. Longer intervals between washing may also help preserve styles. These are some of the reasons that once-weekly or every other week washing is a very real part of many women’s routines. If we want our research to translate into real life, we have to study products in a way that reflects how people actually care for their hair.” added Dr. Frey.
That matters because most anti-dandruff clinical testing has traditionally been built around more frequent washing schedules. In other words, science has not always reflected the way many consumers actually care for their hair.
The key question: Can an anti-dandruff regimen still deliver meaningful scalp benefits -when it is used only once a week?
The answer from this study: yes. In a clinical protocol designed specifically for women of African ancestry who typically wash once per week, a Head & Shoulders shampoo with 1% zinc Pyrithione and conditioner regimen delivered a larger reduction in visible flakes and significant improvement in scalp-health than a non-anti-dandruff shampoo and conditioner.
Beauty Science, Rebuilt Around Her Routine
The study was intentionally built around her routine rather than asking her to fit into a traditional dandruff protocol. That meant washing once per week instead of three or more times per week, including conditioner as part of the wash regimen, and allowing familiar styling products with controls in place so the team could still measure the effect of the treatment.
Participants could use familiar hair styling products such as oil moisturizers, soufflés, oil sheen sprays, and gels, as long as they were applied to the hair and kept at least two inches away from the scalp to help minimize migration. Products like hair grease or braid spray were not allowed on the scalp because they could impact flake assessment, change how the scalp surface looked, or make it harder to know whether a change came from the treatment or the styling product. Participants also stopped using styling products 72 hours before each evaluation so recent product residue would not get in the way of flake grading or scalp biomarker measurements.
"Oils, greases, gels and other styling products are an important part of many textured-hair routines, so simply eliminating them from a study can create an artificial environment and make studies impractical for this population. At the same time, products applied directly to the scalp can create buildup, alter the appearance of scale and make it more difficult to accurately assess dandruff. The goal is not to ignore real-world hair-care practices, but to control for them carefully enough that we can distinguish the effect of the treatment from the effect of the styling products,” added Dr. Frey. .
Before treatment started, everyone completed a two-week “washout,” meaning they used the same non-anti-dandruff shampoo and conditioner to help reset scalp conditions. This reduced the chance that previous routines or products would influence the results. After that, participants moved into the four-week treatment phase comparing the Head & Shoulders shampoo and conditioner regimen with a cosmetic shampoo and conditioner control regimen. The control group mattered because it gave the team a fair beauty-science baseline: it showed what happened with a similar wash routine, but without the anti-dandruff technology, so any added scalp benefit could be more confidently linked to the treatment.
The study followed 31–34 women per treatment group, ages 18–65, who all had visible dandruff and a once-weekly wash routine.
What the Study Found
By Week 2, the once-weekly Head & Shoulders regimen was doing what consumers would hope to see: it reduced visible dandruff more than the cosmetic control. That difference became more apparent with each wash during the 4 week treatment period.
The scalp-health measures helped explain what the graders were seeing. Markers tied to inflammation improved more with the Head & Shoulders regimen.
Human serum albumin, which can appear on the scalp when the surface barrier is stressed, also improved. Together, those measures suggest the scalp was not just looking better from a flake standpoint; it was showing signs of being in better condition.
Consumers noticed some of those benefits, too. At Week 4, women using the Head & Shoulders regimen reported better overall scalp health, less frequent itch between washes, and fewer dandruff symptoms over the prior four weeks.
Why This Matters
Dr. Frey provides perspective on why the study design was important and relevant to the study population; “Representation in clinical research is not only about who is enrolled in a study. It is also about whether the study design accurately reflects how that population actually uses the product. When we account for differences in wash frequency, conditioning and styling practices, the results become much more meaningful to the consumers we're trying to serve.”
For women who wash once per week, scalp care has to last until the next wash day. A regimen that only performs in a three-times-per-week wash model may not answer the question that matters most: will my scalp still look and feel better by the time I get to my next wash day?
Bottom Line
This study matters because it starts with the consumer instead of forcing the consumer into the study design. African American women have historically made up a small portion of typical dandruff studies, even though wash frequency, conditioner use, and styling practices can be very different from the assumptions built into standard protocols. Here, the routine was part of the science.
The result is not a promise that every person will have the exact same experience; clinical studies are controlled, and individual routines vary. But it does give more relevant evidence for women whose wash day happens once a week: anti-dandruff care can be tested—and can work—in a routine that looks much more like real life.
Contributing Authors:
Dr. Cheri Frey, Board Certified Dermatologist and Associate Professor of Dermatology
Tamara Caterino, PhD Senior Clinical Scientist Manager, P&G Beauty Care
Rob Bacon, MBA Senior Clinical Statistician, P&G Beauty Care
John Scarchilli, B.S. Chem Eng, MBA, Director of Scientific Communications, P&G Hair Care
