Last week we talked about the anatomy of skin, and how its structures protect you from the slings and arrows of daily life. Of course, there’s no such thing as a free lunch, and (generally speaking) the side-effects of that protection are the signs of aging.
There are several changes that occur in skin as it ages, and all three layers of the skin (epidermis, dermis, hypodermis) are involved. Well, some of the changes we see in aging skin are actually changes in the deeper tissues of the body — like muscle and bone — which are being revealed through the skin. Starting with the deepest layers of tissue, some of these changes are:
A) Loss of bone and muscle mass
B) Loss of fat in the hypodermis
C) Loss of thickness and elasticity in the dermis
D) Decrease in the area of contact between the dermis and epidermis
E) Loss of pigment cells in the epidermis
F) Accumulation of errors in cell DNA
A) Loss of bone/muscle. It is a key concept of human physiology that all our tissues are in a constant state of flux. For example, the hard matrix of your bones is constantly being absorbed and reformed. This is useful, because it allows tissues to respond to the stresses placed on them (for example, a tennis player’s racket arm has bones that are longer, thicker, and wider than the non-racket arm).
Over time, bones and muscles slowly get smaller and thinner, especially if there is less stress on them (you know, atrophy). It’s subtle, but over time, we lose bone mass in our faces. So as you age, your face is literally changing shape (but your skin isn’t tightening up to match).
B) Loss of fat in the hypodermis. As mentioned in the anatomy article, the hypodermis is a loose layer of fat between the dermis and the underlying muscle. With age, we lose fat cells, but this occurs unevenly (different compartments lose different amounts of fat). As we get older, our cheeks and temples become more hollowed, the upper lip loses volume. And again, we’re left with too much skin for the amount of underlying tissue.
C) Loss of thickness and elasticity in the dermis. Dermis becomes about 6% thinner for every 10 years of age. It also changes at the microscopic level — we lose the proteins that give skin its strength and elasticity, and the remaining proteins are more disorganized. This results in skin that is weaker and more easily injured (because of decreased or poorly functioning collagen protein), and also doesn’t snap back into place as quickly when it is stretched (because of decreased or poorly functioning elastin protein). You can see this in action by gently pinching the skin on the back of your hand. How quickly does it snap (or settle) back into place? As gravity pulls on your skin, this weaker, less elastic skin begins to droop.
D) Decrease in the area of contact between the dermis and epidermis. As I mentioned last week, if you looked at a microscopic picture of the border between the dermis and epidermis, it would look like bubble wrap. With age, it begins to flatten, so it looks more like a flat sheet. This decreases the area of contact between the dermis (blood supply, nutrition delivery) and the epidermis. So cell turnover in the epidermis is slowed down.
E) Loss of pigment cells in the epidermis. Melanin cells in the lowest layer of the epidermis produce pigment, which is then held by all the other cells of the epidermis, giving skin its color. With age, the number of melanin cells decreases (which seems counter-intuitive, I know), and the body’s control over them is decreased. This causes unevenness in skin color, and areas of increased — as well as decreased — pigmentation (e.g., age spots, hyperpigmentation, hypopigmentation).
F) Accumulation of errors in cell DNA. Every time a cell divides, there is a risk of introducing an error into the DNA. So the more times a cell divides (i.e., the longer you live), the more likely it is that an error will occur and won’t be fixed. Ionizing radiation (such as the x-rays that we are exposed to every day from the sun and the earth) does the same thing. DNA errors can lead to cells that are out of control, giving rise to skin growths or cancers.
Many of these signs of chronological aging (A–F) are similar to the signs of photoaging (sun damage). UV light damages collagen and elastin. You actually have more of these proteins, but they are of lower quality, which (1) prevents you from making more “good” collagen and elastin (body thinks it has plenty), and (2) makes skin weaker and less elastic (which is why we get that leathery look). UV light makes skin thicker (a textural change you can see), and of course it also makes your melanin cells misbehave… and damages DNA.
Next week: Common lesions in aging/damaged skin. Then we’ll talk about what you can do about them!
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