I've struggled to find anything at all in the literature that specifically investigates the use of sunscreen as a preventative measure against sun damage in people with deeper skin tones.
Furthermore, I've found almost nothing in the literature that seriously investigates the incident rate of various skin cancers in deeper skin tones. What does exist is mostly made in passing, reviewing general attitudes, or in obscure papers with poor quality control. (Often times the end-points are related to the mortality rate of skin cancers when presented in deeper skin tones, rather than the rate at which they get them or the efficacy of increased melanin content compared to sunscreen to defend against sun damage.)
Current guidelines from the AAD (American Dermatology Association) is that "[p]eople of all colors, including those with brown and black skin, get skin cancer. Even if you never sunburn, you can get skin cancer" and as such "[w]ear sunscreen. Yes, people of color should wear sunscreen."
I found virtually no data from African countries that reviewed skin cancer incident rates, outside of one paper in Ethiopia which looked at Tigray Ethiopians.
One paper I found states that "Public educational campaigns should expand their efforts to educate people of all skin types with emphasis on skin cancers occurring in areas not exposed to the sun (Byrd-Miles et al, 2007), since sunlight is not as important an etiologic factor in the pathogenesis of skin cancer in people of color."
Yet goes on to say "Sunscreen (sun protection factor 30 or greater) should be applied to skin, regardless of complexion, during periods of prolonged exposure, especially during peak hours of sunlight (10 am–2 pm)."
I've seen other such recommendations from other serious papers and organizations, yet I've seen no specific data that looks at how sunscreen plays a role in the prevention of skin cancer in people with deeper skin tones.
Has any research been done that specifically reviews the effects of sun exposure in people with deeper skin tones, the efficacy of sunscreen in the prevention of skin cancer in people with deeper skin tones, and how effective deeper skin tones are in protecting against UVB/UVA?
All emphasis is mine.