zt: The best kind of sunscreen for toddlers

I recommend choosing a "physical" or "chemical-free" sunscreen made with zinc oxide or titanium dioxide — look for one of those ingredients on the label. Unlike chemical sunscreens, which may cause irritation or allergic reactions because the skin absorbs the active ingredients, zinc oxide and titanium dioxide sit on top of the skin, forming a barrier against the sun's rays.

There's no evidence chemical sunscreens are dangerous or toxic, but we just don't know enough yet about how young children react to the ingredients. Also, sunblocks with zinc oxide or titanium dioxide start protecting as soon as you put them on, whereas chemical products need to be slathered on 30 minutes in advance so the skin has time to absorb them.

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 her inner upper arm. If she develops a rash or redness at the site by the next day, choose another formula instead. Also make sure any chemical sunscreen you use is labeled "PABA-free." PABA was once widely used in sunscreens but now has been linked with skin irritation.

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 above 30: Higher 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 since they're usually no different from the adult versions.

When putting sunscreen on your toddler, lay it on thick, making sure every part of her body gets a good coating. Pay special attention to burn-prone areas like the ears, nose, back of the neck, and shoulders. Some sunscreens are 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 if your child stays perfectly still for the rest of the day! In the real world she'll need more sunscreen every two hours or every time she gets wet or is dried off with a towel.

(Note that sunscreen, whether it's based on chemicals or on ingredients that physically block the sun, may instead be called "sunblock" on the label. The terms are used interchangeably by manufacturers.)