system
Given the following post, respond as if you're commenting on Reddit:
human
What changes occur in babies skin between 5 and 6 months that allow for the use of sunscreen?

The go-to rule for sunscreen for babies is 6 months due to the their skin being thin and the surface area ratio for chemicals. What happens at 6 months to make it acceptable to use sunscreen? Is waiting until 6 months even necessary?
gpt
Nothing. The skin gradually toughens up from birth onwards. By 6 months the vast majority of babies are ready. Some would be fine at 5 months or even earlier.  Some might still have a reaction until they're older. They've picked an age where they feel the risk is tiny relatuve to the befefits.