Theoretically, it is investigated why the incidence of malignant melanoma and other skin cancers is increasing, especially in the white-skinned population, despite the fact that people are increasingly using sunscreen cream and wearing sunglasses. The answer is: it is not "although", but "because". When these two agents are used, the melanocytes of the skin on the one hand and the nerve cells of the retina on the other hand transfer to the pineal gland the misinformation of low UV radiation. The melatonin secretion is not increased, as it would be actually necessary and adequate. The feedback cycle of the pineal gland becomes dissociated, and the consequence can be cancer.