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.