Thanks for Visiting: br br Rashguards with a *SPF rating help prevent the incidence of malignant melanoma by safeguarding you from the ravages of the solar rays resulting cellular damage. Melanoma is less common than many other skin cancers. Unfortunately, it is much more detrimental and causes the majority (75) of deaths associated to skin cancer. You can read through more about malignant melanoma on Wikipaedia. br *SPF stands for Sun Protection Factor. The number is determined experimentally indoors by exposing human subjects to a light spectrum meant to mimic noontime sun. Some subjects wear sunscreen and others do not. The amount of light that induces redness in sunscreen-protected skin, divided by the amount of light that induces redness in unprotected skin is the SPF. It is mainly a measure of UVB protection and ranges from 1 to 50 or above.