[cactus2093]

There is evidence that bad (peeling) sunburns as a child are a major risk factor in melanoma. That is never going to be feasible to study in a randomized control trial, in addition to the study taking 40 years to complete it would be unethical to burn children that badly on purpose. Randomized control trials on seatbelts saving lives are also hard to find for the same reason but that doesn’t mean they don’t work.

Also, as anyone who burns easily will be well aware, sunscreen is almost impossible to use properly in the real world. You need to cover every inch of your skin and reapply every 60-90 minutes and make sure not to let it wash off by going in the water too soon or sweating too much, make sure not to rub it off with clothing or towels, etc.

The first part of your advice makes sense in light of this - shade and clothing are much more practical ways to stay safe if you’re outdoors all day and burn easily.

“Use sunscreen sparingly” is just stupid advice to be giving though. There is much more evidence to it helping than doing any harm.