Skin Layers Explained, From the Epidermis to the Hypodermis

The epidermis has its own sublayers. From deepest to outermost:

1. Stratum basale (basal layer). Where new keratinocytes are made. It's also home to melanocytes, the cells that produce melanin, the pigment responsible for your skin tone and your tanning response.
2. Stratum spinosum. Cells here link tightly together. This layer also contains Langerhans cells, which are part of your immune system.
3. Stratum granulosum. Cells begin to flatten and release the fats that will become the mortar of your barrier.
4. Stratum lucidum. A thin, clear layer found only in very thick skin, such as your palms and the soles of your feet.
5. Stratum corneum. The outermost layer of flattened, dead cells held together by lipids such as ceramides. This is what people mean by your skin barrier.

The stratum corneum is where most skin care does its work. Moisturizers soften and seal it, exfoliants loosen its top cells, and when it's damaged you get dryness, stinging and sensitivity. Our dry skin treatment guide covers how to repair it.

Differences in skin tone come mainly from how much melanin your melanocytes make and what type it is, not from how many melanocytes you have. People of every skin tone have a similar number. For help reading your depth and undertone, see our guide to skin tones.

The dermis, where firmness comes from

Beneath the epidermis sits the dermis, which is many times thicker. It's made largely of collagen, which gives skin strength, and elastin, which lets it stretch and recoil. Cells called fibroblasts produce both, along with a gel-like substance rich in hyaluronic acid that helps hold water.

The dermis has two parts:

• Papillary dermis. The upper part, shaped into small ridges that lock into the epidermis above. Its tiny blood vessels nourish the epidermis, which has none of its own. On your fingertips, these ridges create your fingerprints.
• Reticular dermis. The deeper, denser part, with thicker bundles of collagen.

The dermis also contains:

• Blood vessels, which help regulate your body temperature.
• Nerve endings that sense touch, pressure, heat, cold and pain.
• Hair follicles.
• Sebaceous (oil) glands, which keep skin and hair supple.
• Sweat glands, which cool you down.

When collagen and elastin in the dermis break down, wrinkles and sagging follow. That's why the dermis is the real target of most anti wrinkle skin care and of in-office treatments such as lasers and microneedling.

The hypodermis, or subcutaneous layer

The deepest layer is the hypodermis, also called subcutaneous tissue. Some anatomists describe it as tissue beneath the skin rather than part of the skin itself, but it's commonly counted as the third layer. It's made mostly of fat cells grouped together by bands of connective tissue, along with larger blood vessels and nerves.

It has three main jobs. It cushions your body against bumps, insulates you against cold and stores energy. It also gives your face much of its fullness. As you age, facial fat pads shrink and shift, which is part of why hollows under the eyes and folds around the mouth become more visible.

Which skin layer does your skin care reach?

Your barrier exists to keep things out, so most cosmetic products work at or near the surface. Here's roughly where common ingredients act:

• Moisturizers and occlusives: the stratum corneum, where they reduce water loss and soften the surface.
• Exfoliating acids: the upper epidermis, where they loosen dead cells.
• Retinoids: absorbed into the epidermis, where they change how cells behave, with effects that reach collagen in the dermis over months of use.
• Sunscreen: stays on the surface, filtering UV before it reaches living cells.

Sunlight affects more than one layer. UVB acts mainly on the epidermis and causes sunburn. UVA penetrates deeper into the dermis, where it contributes to wrinkles and loss of firmness. Both play a role in skin cancer, which is why a broad-spectrum sunscreen for your face matters all year.

How the layers of skin change with age

Every layer shifts over time. The epidermis renews more slowly, so skin can look duller and wounds take longer to heal. The dermis makes less collagen and elastin and becomes thinner, which shows up as fine lines and laxity. Oil glands produce less sebum, so many people find their skin gets drier. The hypodermis loses volume in the face while often gaining it elsewhere on the body.

Sun exposure speeds up many of these changes, which is why two people of the same age can have very different skin. Daily sun protection is the single most useful way to slow them.

Questions people ask

How many layers of skin do humans have?

Humans have three main layers of skin: the epidermis, the dermis and the hypodermis. The epidermis has four or five sublayers of its own, depending on where on the body you look.

Which layer of skin is the thickest?

The dermis is usually much thicker than the epidermis. The hypodermis varies the most from person to person and place to place, since it depends on how much fat is stored there.

Which layer of skin gives skin its color?

Skin color comes mainly from melanin, which is made by melanocytes in the basal layer of the epidermis. Blood flow in the dermis and pigments such as carotene also add to your overall tone.

Which skin layer do scars form in?

Injuries that stay in the epidermis usually heal without a scar. Wounds that reach the dermis are more likely to leave one. See a doctor for cuts that are deep, gaping or won't stop bleeding.