I recommend choosing a "physical" or "chemical-free" sunscreen made with zinc oxide or titanium dioxide. (I also suggest keeping a baby younger than 6 months out of the sun altogether whenever possible. When that's not feasible, be sure to protect your young baby with sunscreen.) (We recommend this too and use your Shaidee Sun Cover.)
Zinc oxide and titanium dioxide sit on top of the skin, forming a barrier against the sun's rays. Sunscreens with zinc oxide or titanium dioxide start protecting as soon as you put them on.
Chemical products, on the other hand, need to be slathered on 15 to 30 minutes in advance to give the skin time to absorb them. They may cause irritation or allergic reactions because the skin absorbs the active ingredients.
There's no evidence that chemical sunscreens are dangerous or toxic, but we just don't know enough yet about how young children react to the ingredients.
If you do use a chemical-based sunscreen, do a patch test first to make sure your child won't have a reaction to it. Apply a small amount to the inside of the upper arm. If your child develops a rash or redness at the site by the next day, choose another formula instead.
You may have heard you should look for a "broad-spectrum" product that protects against both UVA and UVB rays. Any sunscreen that contains the physical blocker zinc oxide or titanium dioxide will do this.
The sun protection factor (SPF) should be at least 15, but you generally don't need to go higher than 30: Over than that and you're getting smaller and smaller amounts of added protection – which, in a chemical sunscreen, means a higher dose of unwanted chemicals.
It's fine to use a "children's" sunscreen, but don't go out of your way to buy one of these. They're usually not different from the adult versions.
Lay the sunscreen on thickly, making sure every part of your child's body gets a good coating. Pay special attention to burn-prone areas like the ears, nose, back of the neck, and shoulders. Some sunscreens have a bright tint when you apply them and then fade to clear in a few minutes, making it easier to tell if you're covering every inch of your child's vulnerable skin.
Reapply sunscreen often. Waterproof sunscreens may be slightly hardier than other products, but don't trust a label that promises to protect for eight hours. That's only accurate if your child stays perfectly still for the whole day! In the real world he'll need more sunscreen every two hours or every time he gets wet or is dried off with a towel.
Note that while zinc oxide and titanium dioxide are typically known as "sunblocks," other sunscreens (whether based on chemicals or on ingredients that physically block the sun) may also have the word "sunblock" on the label. The best way to know what you're getting is to check the label for ingredients.