People who use a high level of sun protection factor (SPF) tend to spend more time in the sun, but may not reapply their sunscreen as needed. The result is a higher risk of skin damage, accelerated skin aging, and a greater chance for harmful skin lesions.

For example, one double-blind randomized trial studied the use of different levels of SPF protection while being out in the sun. Results showed that depending on the level of SPF protection used, proper sunscreen reapplication was often overlooked.

The study assigned 87 individuals to either a low SPF (SPF 10) or a greater SPF (SPF 30) sunscreen and required the subjects to use their sunscreen on a daily basis throughout a summer holiday. The researchers measured multiple variables including time spent in the sun, sunscreen application behaviors, reapplication behaviors, and any resulting sunburn or sun-related skin damage.

Those who used the higher SPF spent longer durations in the sun than those who used the lower SPF. The researchers found that depending on how the participant’s skin felt in the sun, and how “safe” the SPF was mentally registered to be, those believing to have better sun protection with a higher SPF spent more time in the sun. However, those individuals tended to forget or put off the process of reapplying their SPF in a timely manner, resulting in a higher rate of sunburn and skin damage compared to those who used the lower SPF.

The failure to properly reapply sunscreen while being out in the sun for longer durations of time makes for an increased probability of skin damage and accelerated skin aging, the authors concluded.

No matter how high of an SPF is used, recommendations are to stick with hourly SPF reapplication for activities in the sun, post-water activity, and for post-sweating activity. As reported in other dermatologist-authored studies, the year-round use of broad-spectrum sunscreens, wide-brimmed hats, long sleeved shirts, and the avoidance of both peak sun exposure and UV tanning beds is also recommended for optimal sun protection and better skin health.

Reference: Autier P, Dore ́JF, Ne ́grier S et al. Sunscreen use and duration of sun exposure: a double-blind, randomized trial. JNCI. 1999: 91(15); 1304-1309.