We're in the middle of summer and still feeling the the fiery wrath of the sun. Obviously, you've heard that too much sun sucks for your skin — from the immediate issue of sunburns to long-term problems such as wrinkles and skin cancer. But how bad is one sunburn, really? Does it actually change your skin? Yes, it does, says Jennifer Stein , MD, PhD, of NYU Langone Medical Center. We talked to Dr. Stein to find out what exactly is happening to your skin when it's exposed to the sun.The energy that comes from the sun is UV light. "That extra-high energy can cause mutations in your genes," explains Dr. Stein. Although that doesn't happen immediately to all of your skin cells, every bit of exposure to sunlight throughout your life adds up to increase your risk for mutations."If you have enough mutations in [the DNA of] a skin cell," Dr. Stein adds, "that’s how you get skin cancer."Researchers have been able to sequence the DNA from cells within cancerous tumors and have found that UV damage leaves its own characteristic pattern of mutations . But we can also be born with other mutations, such as the one often responsible for having sun-sensitive fair skin as well as red hair. With enough mutations, you'll end up with skin cancer."The redness of a sunburn is usually caused by the UVB portion of sunlight," Dr. Stein says. "The high energy of UV light causes inflammation in the skin that looks red and warm." Over time, the inflammation will heal, the burn will fade, and some of the sun-damaged cells will die and peel away. But an especially severe sunburn can limit your ability to sweat and can make you feel sick . You might even feel a little cold or have chills.A single sunburn does slightly raise your risk for melanoma , the most serious kind of skin cancer. If you've had five sunburns, your risk for melanoma is doubled. However, it's also good to remember that melanoma is quite rare, accounting for only 1% of all skin cancer cases . So, of course, sun damage is something you should try to avoid as much as possible. But accidentally getting a sunburn every once in a while is understandable and probably isn't the end of the world.Even if you're not in the sun long enough to burn, that exposure can still do some damage. Melanin is your skin's natural protection against sun damage. Because tanning increases the amount of melanin in your skin (making it a bit darker), "we used to think tanning was good and burning was bad," says Dr. Stein. But more recent research has revealed that the amount of melanin we produce when we tan just isn't enough to outweigh the damage.Even if you're an indoor-tanning addict , it's never too late to stop. Your body will thank you.Slathering on your SPF of choice is definitely a good move. But to get the most out of your sunscreen, experts generally recommend using enough to fill a shot glass and reapplying every two hours (and again after you've been swimming). So, we certainly couldn't blame you for slacking off a little bit. "That's why you don’t want sunscreen to be the center of your whole sun protection plan," says Dr. Stein. Instead, she recommends wearing clothes (including big floppy hats) that cover you up so you don't have to worry about reapplying — and taking breaks from the sun every once in a while.