You slap on some sunscreen, head out the door, and feel like you’ve done everything right. But is your skin actually getting the protection it needs? Here’s a full breakdown—from filter types to SPF numbers and the spots that are easy to forget, with clear dos and don’ts along the way.

Not all sunscreens work the same way, and it comes down to the filters they contain.

There are two types. Physical (mineral) filters like zinc oxide and titanium dioxide sit on top of your skin and reflect UV rays away. They act instantly. The downside is that they can leave a white cast, particularly on darker skin tones. However, newer formulas are getting much better at blending in.

Chemical (organic) filters work differently. They absorb UV rays, convert their energy into heat, and release that heat from your skin. They’re usually lightweight, comfortable under makeup, and often more water-resistant. The catch: they need about 20-30 minutes to activate after you apply them. Also, some chemical filters like oxybenzone, homosalate, and octinoxate have been associated with potential health risks.

Can’t choose between the two types of filters? Plenty of sunscreens blend both, and that’s a perfectly good option. If you’re not sure what’s in your sunscreen, an ingredient checker can help. The app analyzes the formula and lets you avoid potentially unsafe filters.

Once and for all: the SPF number doesn’t tell you how long you can stay in the sun. To understand the difference between SPF 30 vs 50, start here: it’s not about time, it’s about how much UV exposure your skin is protected from. SPF 30 blocks around 97% of UVB rays, while SPF 50 blocks about 98%. This gap isn’t dramatic, but it matters—especially since most people apply less sunscreen than they should. And no sunscreen blocks UV rays completely, no matter how high the number.

So how do you pick the right one?

Think about how you’re actually spending your day. SPF 30 is usually fine for everyday city life. For beach days, outdoor workouts, or if you burn easily, dermatologists recommend SPF 50 or higher. And if you use retinoids or acids in your skincare routine, your skin becomes more sensitive to UV damage, so SPF 50 every day is non-negotiable.

1. Choose broad-spectrum. This means protection from both UVB rays, which are primarily responsible for sunburn, and UVA rays, which are mainly associated with skin aging. Both UVA and UVB rays can damage the DNA in skin cells and increase the risk of skin cancer. If the label doesn’t say broad-spectrum, pick a different one.

2. Apply enough. For the face alone, you need about a quarter teaspoon, which is roughly the size of five peas. If you use far less than that, the sunscreen can’t form a proper protective layer. As a result, you end up with only a fraction of the SPF stated on the label.

3. Remember the easy-to-forget spots. Neck, ears, hands, lips, and the skin along the hairline all need protection just as much as your face. Lips have delicate skin and almost no melanin, the pigment that gives skin some natural UV protection. The neck tends to have thinner skin, making it more vulnerable to UV damage. Hands are constantly exposed to sun, water, and detergents, which wear down the skin barrier.

4. Reapply every two hours. UV filters break down with sun exposure over time, so the protection you applied in the morning doesn’t last all day. Reapply more often if you’re swimming or sweating, because even water-resistant formulas don’t hold up after drying with a towel.

5. Use it year-round. Clouds block visible light but not UV rays entirely, which means you can still get UV exposure on an overcast winter day.

1. Don’t rely on SPF makeup alone. Foundations and BB creams with SPF are a nice bonus, but the amount you realistically apply to your face just isn’t enough for full sun protection.

2. Don’t skip reapplication because you’re wearing makeup. SPF wears off after about two hours, with or without a full face of makeup. SPF sticks and powder sunscreens are designed specifically for this situation: they layer over makeup without smudging or ruining your look.

3. Don’t settle for a sunscreen you dislike. If it’s greasy, too heavy, or leaves a white cast, you’ll probably use too little and never reapply. The sunscreen that actually works for you is the one you’ll use consistently. So it’s worth trying different textures until you find one you actually like.

4. Don’t assume higher SPF means longer protection. SPF 70 doesn’t last twice as long as SPF 30. All sunscreens break down over time and need to be reapplied on the same schedule.

5. Don’t skip sunscreen, no matter your skin tone. Darker skin has more melanin and is less prone to sunburn, but UV damage, premature aging, and skin cancer are still real risks.

Pick a broad-spectrum formula that works for your skin type, use enough of it, and reapply regularly. That’s really the whole strategy. Find a sunscreen you actually enjoy using and make it part of your daily routine.