Sun Protection Factor (SPF) is a measure of how long a sunscreen protects from ultraviolet rays. Using SPF 30 means it will take 30 times as long for skin to burn than with no sunscreen. "SPF" refers to sunscreen’s ability to protect from UVB rays, which cause sunburn and skin cancer. Higher SPF provides better protection over longer time. UVA rays cause skin aging. Lip balms with SPF protect sensitive lip skin, reapply frequently. Generously apply sunscreen 15 minutes before going outdoors.
SPF 30 blocks 97% of UVB rays, SPF 50+ blocks 98%. Although SPF 100 protects somewhat more, it must be reapplied as often as lower SPFs. SPF measures protection compared to unprotected skin. For example, SPF30 allows 3.3% of UVB to reach skin, SPF50 allows 2%. Experts recommend SPF 30 sunscreen. Numbers tell time before skin reddens, called erythema. With SPF 15, stay in sun 15 times longer than bare skin.
What is the meaning of SPF 50?
The number tells time before skin reddens without protection, called erythema. Using SPF 50+ blocks 98% of UVB rays. PA+++ means UVB protection rate is 98%, lasts 500 minutes on skin, blocks 90% of UVA rays.
Higher SPF provides better protection over longer time. Using the right SPF protects from UV rays.