Visible light and melasma
Ultraviolet radiations are considered the main causative factor of
the relapses in melasma and a strict avoidance of sun exposure is
recommended. However, despite the use of very effective sunscreens against UV radiations, many patients have relapses of the
hyperpigmented lesions after the summer period. Interestingly, it
has been recently shown that the visible light was also able to
induce an increase of skin pigmentation, at least in dark skin types.
Indeed, the effect on pigmentation of visible light was compared
with UVA exposure in the back of healthy volunteers. In dark skin
patients (skin type IV–VI), both UVA and visible light were able
to increase pigmentation, but the pigmentation was more intense
and more stable after visible light exposure as compared with
UVA.2
Those results demonstrate that visible light is also able to
modulate the pigmentation process. According to these results, we
cannot conclude that visible light plays a role in melasma relapses,
but it is tempting to hypothesize that it could explain the onlypartial protective effect of most sunscreens. Thus, the use of tinted
mineral sunscreens could protect both against UV and visible
light, and might be more effective for preventing the melasma
relapses. Prospective comparative trials should be performed to
answer to this very practical but crucial question.