Taking care of your skin is probably second nature by now. You know to slather on SPF each morning and scan for new and changing moles to keep your skin happy and healthy. But despite understanding how to combat wrinkles and ward off disease, there’s a fair share that you might not know about your body’s largest organ. Read on for seven interesting facts about your skin.

1.  Your skin’s appearance and texture can give you clues about the rest of your health.

Sometimes, changes in your skin can signal changes in your health as a whole. For example, according to Brooke Jackson, MD, Director of the Skin Wellness Center of Chicago, “The hormones that the thyroid produces are directly responsible for the natural fats that protect the skin, as well as hair and cell growth and hair pigmentation.”

She explains that in a person with hyperthryroidism (when the thyroid overproduces thyroid hormone), the epidermis––the outer layer of skin––may thicken and skin may be soft. With hypothyroidism (when the thyroid under-produces thyroid hormone), on the other hand, symptoms include very dry skin and thickened skin on the palms and soles. Another way your skin can tip you off to health issues: Acanthosis nigricans, a condition in which skin around the neck darkens and changes in texture, is often associated with diabetes, according to D’Anne Kleinsmith, MD, dermatologist at William Beaumont Hospital in Royal Oak, MI.

2.  Everyone has the same pigment in their skin that’s responsible for color. 

Melanin, explains Josie Tenore, MD, SM, is a coloring pigment that is present in all people’s skin—regardless of race. “The difference in skin tone between people of different races—and between people of the same race––lies in how much of this pigment is present, and its distribution within the skin.”

More specifically, everyone—no matter how dark or pale they are––has the same number of melanocytes, which are the cells that make melanin, explains Arnold Oppenheim, MD, a board-certified dermatologist. “It’s their product, melanosomes—which contain the melanin––that differ. Some people have denser and larger ones, which make their skin darker.” Also, the denser and closer together they are, “the more protection the skin is afforded from skin cancer,” he says.

3. As we age, our skin sheds cells more slowly.

Ever wonder why children have such naturally rosy and dewy skin? While skin of all ages produces new cells which eventually move to the surface and shed off, young people’s skin does this more often, according to Dr. Tenore. “In kids, this happens every two to three weeks, which gives them that vibrant, shiny skin. But as we age, this process becomes slower. More dead cells stay on the surface, resulting in that dull, dehydrated look.”

She adds that exposure to direct sunlight slows down the sloughing off process even further because UV light decreases cellular turnover. Depending on your skin type—your dermatologist can identify yours––daily exfoliation or a topical antioxidant serum that contains retinoids, vitamins and peptides can help encourage cell turnover, according to Francesca Fusco, MD, a New York City dermatologist.

4. Stretch marks can be prevented—to a degree.

Pregnancy, weight fluctuations and even teenage growth spurts can all cause stretch marks, those squiggly lines that start out darker than your skin color and often appear on the hips, thighs and abdomen (but can crop up anywhere). When collagen and elastin initially break down, says Dr. Oppenheim, skin creates striae rubrae—red or purple stretch marks on light-colored skin—due to inflammation. When stretch marks are in this phase, applying retinoid creams to them—no matter where they appear––can “considerably lessen their appearance,” says Dr. Fusco. That’s because the medication promotes cell turnover and skin regeneration. Some older stretch marks, which are lighter in color and have indentations, can be treated with lasers to help smooth the skin, says Dr. Kleinsmith, but it depends on where they appear—ask your dermatologist if lasers can help reduce the appearance of your older stretch marks.

5. The oiliness of our skin dictates what type of hair grows in that area.

The relationship between hair and skin is a close one. “The whole sebaceous (oil) gland and hair apparatus is one unit,” says Dr. Oppenheim. “The oil gland grows out of the hair follicle, which it helps to lubricate.” But it’s the difference in the individual glands that affects hair type. According to Dr. Oppenheim, “Where we have large oil glands, which produce more oil, we have thin hairs; where we have small oil glands, which produce less oil, we have thick hair.” People have oily skin in the middle of their faces because there are large sebaceous glands there, and they have dry skin on the periphery because there are small oil glands there. This is why even men with heavy beards don’t grow hair in the middle of their faces.  

6. Age spots should really be called “sun spots.”

Those brown spots that tend to crop up with age have little to do with the passing years, and much more to do with soaking up rays. “Age spots are the result of cumulative sun exposure and subsequent damage,” says Dr. Fusco. “They appear because pigment cells have accumulated in the top layer of skin.” To prevent sunspots, apply sunscreen in the morning every single day—and every few hours afterward if you’ll be in direct sunlight. “The minimum SPF you should use is 30; be sure that it’s broad spectrum to block UVB and UVA rays.” advises Dr. Fusco. Aim to use a marble-sized amount of block for your face and a shot glass–sized amount for your body. Though age spots aren’t directly related to age, seborriheic keratosis, benign hereditary moles that usually stick out from your skin, are. They vary in color from white to black, says Dr. Oppenheim, and tend to appear on the face, scalp and torso (but can show up anywhere except your palms, the soles of your feet and your mouth) as you grow older.

7. Melanomas don’t always have color.

If you’re on the lookout for dark moles to screen for skin cancer, you’re on the right track. But malignant spots aren’t always so easy to find. “Follow the Sesame Street rule—‘One of these things is not like the other,’” says Barbara Reed, MD, a dermatologist at the Denver Skin Clinic. “Melanomas can be red, purple, flesh-colored or even white. I think I’ve seen them in every color except green,” she explains. If a mole looks funny, grows, itches or just plain makes you obsess over it, Dr. Reed recommends heading to your dermatologist for a check-up. And always tell your doctor about any other new spots or skin irregularities that you notice.