Unlike direct DNA damage, which occurs in areas directly exposed to UV-B light, reactive chemical species can travel through the body and affect other areas—possibly even inner organs.  The traveling nature of the indirect DNA damage can be seen in the fact that the malignant melanoma can occur in places that are not directly illuminated by the sun—in contrast to basal-cell carcinoma and squamous cell carcinoma, which appear only on directly illuminated locations on the body.