Abstract: The invention relates to a device for protecting a skin area against light when detecting and/or treating skin disorders, especially cancer and its preliminary stages, including application of compounds and/or compositions to the skin, in connection with which a photoreactive substance appears in the skin area. The device comprises an opaque foil (1) forming a cavity (4) relative to the skin and having edges (3) engaging the skin, the width of the edges (3) being determined by formula (I), wherein m=the width of the edge, &dgr;=the penetration depth of the light in the skin, In=the natural logarithm, t=the time of the effect of the light, I0=the luminous intensity at the skin surface, and Ddiffused=the diffused energy dose which is allowed to reach the skin area concerned.

Abstract: The invention relates to a method for detecting cancer on skin of humans and mammals by picturing spectroscopy. The method includes that delta aminolevulimic acid ALA is applied on the skin on that area where cancer is suspected to be present, the substance is removed after 1 to 24 hours, and the area is illumiated with light having a wave-length of 330-440 nm and the fluorescent irradiation which arises is registered and evaluated, which radiation has a wave-length 610-715 nm. The invention also includes an arrangement for performing the method.