The question refers to tanning that involves UV exposure.

The debate has been going on forever whether UVA radiations are less dangerous than the UVB. In the past years scientists have striven to prove that both types of radiations are dangerous for health, long-term cancer generators, fighting the existing theories that only UVB are dangerous for health. This might be a normal "freak out" reaction to the increase in skin cancer cases.

What do we know about UV radiations? That they are differentiated according to wavelength into UVA (400-320nm), UVB (320-290nm), UVC (290-100nm). It seems that contrary to what we are inclined to believe, the longer the wave, its effects are milder on the skin.

UVA radiations might be beneficent after all! Recently, a group of Australian researchers have completed a study on the basis of a twelve-months experiment on five groups of guinea-pigs, exposed to various types of UV radiations and one group was not exposed to radiation at all. The animals had been subjected to DMBA-induced melanocytic nevi similar to human nevi. The result was that there was a significant increase in nevi in the animals exposed to UVB compared to all groups while the ones exposed to to full solar spectrum experienced a nevi decrease. Thus, a conclusion may be drawn – that it is possible that visible light /broad-band UVA not only does not affect melanocytic nevi but it may be inhibitory for nevi induction.

So, following our question in the beginning, in the light of this study, the answer might be that sun tanning between intervals that allow mostly UVA radiations (until 10 AM and after 4 PM) and exposure to UVA solariums may be not all that deleterious after all.