Sunscreen basics: SPF, broad spectrum and how much to use

If you only add one step to your routine, make it sunscreen. Daily sun protection helps prevent sunburn, and it reduces the sun damage that shows up over the years as dark spots and fine lines. Here is what the labels mean and how to use it well.

What SPF measures

SPF stands for sun protection factor. It shows how well a sunscreen protects against UVB, the part of sunlight that causes most sunburn.

The numbers do not grow in a straight line. According to the American Academy of Dermatology, SPF 30 filters about 97% of UVB rays and SPF 50 filters about 98%. No sunscreen blocks all of them. A higher number helps, but how you apply it matters more.

Why "broad spectrum" matters

Sunlight also contains UVA. UVA goes deeper into the skin and contributes to dark spots and visible aging. It also passes through window glass. A sunscreen labeled broad spectrum protects against both UVA and UVB.

Look for three things on the label:

1. Broad spectrum
2. SPF 30 or higher
3. Water resistant, if you will swim or sweat

Mineral or chemical filters

Both types work when you use them correctly.

1. Mineral filters (zinc oxide and titanium dioxide) sit on the skin and reflect and scatter UV light. They are often a good choice for sensitive skin. Some leave a white cast, especially on deeper skin tones.
2. Chemical filters absorb UV light. They usually feel lighter and leave no white cast.

The best sunscreen is the one you like enough to wear every day.

How much to use

Most people apply much less sunscreen than the amount used in SPF tests, so they get less protection than the label shows. For the face and neck, use a generous layer that covers every area, including the ears, the hairline and the sides of the nose. Some people use two full finger-lengths of lotion as a guide.

If you use a moisturizer with SPF, check that you apply enough of it. A thin layer of moisturizer does not give the SPF on the bottle.

When to apply and reapply

1. Apply sunscreen as the last step of your morning routine, before makeup.
2. Use it on cloudy days too. Clouds block only part of the UV light.
3. Outdoors, reapply about every two hours, and right after swimming or sweating.
4. Sunscreen is one part of sun protection. Shade, a hat and sunglasses help too, especially around midday.

Sunscreen and your routine

In the Glowinout app, sunscreen is part of the morning routine. Your routine shows the products picked for your skin and how to use them.

Glowinout gives cosmetic guidance, not medical advice. If you notice a new or changing spot or mole, see a dermatologist.