What effect do UV-B rays have on the skin?

UV-B rays are primarily responsible for causing sunburn because they penetrate the outer layer of skin and can damage the DNA in skin cells. This type of radiation is more intense than UV-A rays and is particularly effective in triggering inflammatory responses, which lead to redness, pain, and the characteristic peeling associated with sunburn.

Sunburn is a clear indication that the skin has been harmed by excessive UV-B exposure, leading to an increase in melanin production as part of the skin's natural defense mechanism, which is not as direct as the effect described in the other options. While UV-B rays do play a role in skin darkening, by stimulating melanin production, that is more of a secondary reaction rather than the primary effect of these rays. Moreover, UV-B rays do not contribute positively to skin elasticity; rather, prolonged exposure can lead to damaging effects on the skin's structure and overall health.