As a New York City dermatologist, I see all manner of skin problems walk into my office. And while my job is to help my patients to fix those issues, a big part of that is also deducing why they are happening. Think of it as skin care forensic science—I’m investigating the clues to solve the complexion crimes that got you into trouble in the first place.

With that in mind, here are the 10 most common skin care mistakes to avoid if you want to keep your skin on the right side of the (beauty) law.

Wear sunscreen whenever you are in the sun—no matter how long that may be.

The biggest anti-aging tip any dermatologist will give you is a preventative one: Protect yourself from the sun. But people tend to think if they aren’t going to be staying out in the sun, they don’t need to apply it. Like the suburban mom, driving around town on errands, or the office worker grabbing lunch and a breath of fresh air—they don’t plan on spending extended periods of time outside, so they don’t think to wear SPF. The thing about your skin is it doesn’t care how long you are in the sun—any exposure, no matter the length of time, is still damage. Five minutes here, 10 minutes there—it all adds up the same.

Think of it this way: If you spend 30 minutes a day in the sun without protection, over the course of the summer, that is the damage equivalent to spending two full days in the sun. Keep your skin covered while you’re out and about by using a moisturizer with SPF — it’s an easy way to work sun protection into your daily routine.

Apply your sunscreen before you are in the sun.

If you are already wearing sunscreen on a daily basis, then you are one step ahead of the game. However, there’s more to it than that—if you aren’t applying it right, you could still be putting your skin in harm’s way. A big mistake I see is people who wait to apply their SPF until they are already in the sun. Your skin isn’t fully protected until the sunscreen has had a chance to settle and become active. In order to make sure you have the full strength of that SPF working for you, apply it 10-15 minutes before you plan to go outside. Remember to protect often overlooked areas like your ears and lips. Also, classically neglected is the top of your forehead adjacent to the hairline because people fear messing up their hair if sunscreen is applied there. Due to this neglect, the top of the forehead is where I see an epidemic of pre-cancers, skin cancers and sunspots in my practice.