Summary Background Human skin protects the body from external damage, pathogens and oxidative stress factors such as ultraviolet (UV) radiation. Excessive exposure to UV radiation can lead to increased production of free radicals and hence to skin damage such as inflammation, premature skin ageing and skin cancer. Besides UV, the visible and near infrared (NIR) regions are also a source of radical production. Half of all free radicals are induced by the visible + NIR region of the solar spectrum in people with skin types I–III, but data on the effects in people with skin types IV–VI are missing. Objectives This in vivo pilot study addressed the distribution of radical production in skin types IV and V during irradiation in the UV, visible and NIR spectral regions, comparing the first results with those of skin type II. Methods The measurements were performed in vivo using L‐band electron paramagnetic resonance spectroscopy and the spin probe PCA. Results In skin types IV–V most radicals were induced in the visible + NIR region, followed by the NIR and UV regions of the sun spectrum. Significantly (P ≤ 0·05) more radicals were induced in skin types IV–V than in type II during NIR irradiation, whereas skin types IV–V exhibited significantly less UV‐induced radicals (P ≤ 0·01) than skin type II. Conclusions All spectral regions (UV, visible and NIR) cause free radical formation in skin types II and IV–V. After 4 min of solar‐simulated exposure (UV‐NIR), the radical formation in skin types IV–V is 60% of that in skin type II. Therefore people with darker skin types also need solar protection. What's already known about this topic? Excessive exposure to ultraviolet (UV) radiation can lead to increased production of free radicals and hence to skin damage such as inflammation, premature skin ageing and tumour progression. The visible and near infrared (NIR) regions of the solar spectrum also induce radicals. Half of all free radicals in skin types I–III are due to visible + NIR exposure, but data about the effects in skin types IV–VI are missing. What does this study add? This in vivo pilot study addresses the distribution of radical production in skin types IV and V during irradiation in the UV, visible and NIR spectral regions, comparing the results with those of skin type II. The results provide the first ideas of possible long‐term effects of excessive exposure to visible and NIR radiation in skin types IV and V. What is the translational message? In people with skin types IV–V, significantly more radicals were formed during NIR irradiation compared with skin type II. As in skin types IV–V the NIR values reach or exceed those of the UV and visible, which could influence premature skin ageing and carcinogenesis. Individuals with skin types IV–VI might need a different type of sun protection from those with skin types I–III to avoid subsequent damage by solar radiation. Respond to this article Linked Comment: Young. Br J Dermatol 2019; 180:456–457. Plain language summary available online