What primarily causes sunburns and skin cancers?

UVB rays are primarily responsible for causing sunburns and increasing the risk of skin cancers. These rays have a shorter wavelength compared to UVA rays and are more intense, particularly during peak sunlight hours. UVB rays penetrate the superficial layers of the skin, directly damaging the DNA in skin cells. This damage can lead to inflammation, which manifests as sunburn, and can also trigger mutations that contribute to the development of skin cancers over time.

While UVA rays penetrate deeper into the skin and can also contribute to skin aging and some types of skin cancer, they are less associated with immediate sunburn. Infrared radiation and visible light do not significantly contribute to sunburn or skin cancers and primarily have different effects on skin and health. Thus, UVB rays are the primary concern in the context of sunburn and carcinogenic effects.