There's another reason to avoid sunscreens with SPF over 50 -- they tempt people to apply too little sunscreen and stay in the sun too long. Your skin may be protected by UVB rays that cause sunburn, but could leave your skin exposed to damaging UVA rays that cause other kinds of damage.
The U.S. Food and Drug Administration has proposed prohibiting the sale of sunscreens with SPF values greater than 50+, calling higher SPF values “inherently misleading” due to the false sense of security that higher numbers impart. But the FDA has not issued a regulation that carries the force of law.
When used correctly, sunscreen with SPF values in the range of 30 to 50 will offer strong sunburn protection, even for people most sensitive to sunburn. Consumers should avoid sunscreen products labeled with anything higher than SPF 50+ and reapply sunscreen often, regardless of the SPF.