UVB is ultraviolet (UV) radiation produced by the sun that has a shorter wavelength. It is linked to the tanning, sunburning, and/or blistering of the skin caused by the sun. It damages the outermost layers of your skin.

Sun Protection Factor (SPF) is a number rating that informs you the level of sunburn protection from ultraviolet B (UVB) radiation in sunscreen products. A different scale is used for longer wave ultraviolet A (UVA) radiation.

An SPF of at least 30 blocks 97% of the sun's UVB rays. The American Academy of Dermatology Association and many dermatologists recommend using a sunscreen with at least SPF 30. While this seems adequate, consumers typically apply only one-third (1/3) to half (1/2) of the amount of sunscreen that is needed to achieve the advertised SPF. So, some sunscreen users may not get the sun protection they need to prevent sunburn and skin cancer.

A higher-number SPF product blocks slightly more of the sun's UVB rays and may be useful in people with very light skin tone or other conditions that make their skin more sensitive to the sun.

No sunscreen can block 100% of the sun's UVB or UVA rays.

A high-number SPF product allows a person to spend longer in the sun without burning but needs to be reapplied as often as a lower-number SPF product. Generally, it is recommended that sunscreen should be reapplied approximately every two hours and after swimming or excessive sweating.