Layers of Human Skin

How many layers are in human skin?

The 8 main layers of the skin.

How many layers the skin has depends upon what area of the body you are in.

Most of the surface area of the human body has 7-8 layers of skin.

The 8 layers of the skin are (from top to bottom):

Stratum corneum (SC)

Stratum lucidum (only in palms and soles)

Stratum granulosum (Granular layer)

Stratum spinosum

Basal Layer (deepest layer of the epidermis)

Papillary Dermis

Reticular Dermis

Hypodermis/ Fat layer

How many layers does the epidermis of the skin have?

The epidermis has 4- 5 layers of skin.

The palms and soles have 5 layers which include a stratum lucidum.

The rest of the skin does not have a stratum lucidum and only has 4 layers.

The lip skin has a very thin stratum corneum that is hardly a layer at all. In fact, some say the lip does not have a statum corneum- but the lip does have 2-3 cell layers on the surface that can be considered the stratum corneum.

How many layers does the dermis of the skin have?

The dermis has two layers:

the reticular dermis

the papillary dermis

Where are stem cells found in human skin?

The skin is made of two main layers: the epidermis and the dermis. Each has a different type of stem cell.

The reticular dermis has stem cells with different characteristics than the stem cells in the papillary dermis.

The stem cells in the dermis move around but tend to stay in their own section of the dermis. [1]

Which layer of the skin has the skin barrier?

The skin barrier is found in the stratum corneum layer of the epidermis.

What skincare ingredients can penetrate the skin layers?

Peptides, stem cells, collagen, elastin and other ingredients in skincare products cannot penetrate into the skin and are a waste of money [2].

The reasons that these ingredients cannot penetrate the skin are usually because they are too big or too hydrophilic.

Even if peptides, stem cells, collagen and elastin are placed in nanotechnology or other delivery devices, they cannot penetrate into the skin.

This is why many researchers are trying to use micro-needling techniques to increase the penetration of stem cells and peptides into the skin.

What skincare ingredients penetrate into the epidermis?

Most skincare ingredients can only penetrate into the uppermost layers of the epidermis.

This is because the skin barrier is designed to keep things out.

Skincare products such as sunscreens, moisturizers, hydrating facial serums with humectants and exfoliants target the epidermis and do not need to get into the dermis to have a beneficial effect.

What skincare ingredients penetrate into the dermis?

To have an effect on wrinkles and skin pigmentation, skincare ingredients must penetrate into the dermis.

Very few cosmetic ingredients can penetrate into the dermis of the skin because only ingredients smaller than 500 Da [3] can penetrate into the dermis of the skin.

Some skincare ingredients, such as defensins, can get into the skin via the hair follicle.

Hormones and retinoids can penetrate easily into the dermis of the skin. Hyaluronic acid fragments smaller than 500 Da can penetrate into the skin, but longer HA chains cannot [4]. The vast majority of peptides are larger than 500 Da and cannot penetrate into the skin.

Which moisturizers penetrate into the skin?

Humectants can penetrate into the upper layers of the epidermis.

Occlusive moisturizers stay on the skin’s surface.

The lipids in barrier repair moisturizers can penetrate into the upper layers of the epidermis to repair the skin barrier.

Moisturizing oils may penetrate into the skin depending upon what types of fatty acids they contain. (See oil discussion below.)

Moisturizers do not penetrate into the dermis, however, the epidermis layer is responsible for skin hydration and is the target of moisturizing ingredients.

Which serums penetrate into the skin?

Hyaluronic acid serums made of low molecular weight HA (short chains of HA) penetrate into the epidermis and can help other ingredients penetrate into the

epidermis. HA is known as a penetration enhancer ingredient [6], however, HA does not penetrate all the way to the dermis. The only serums that penetrate into the dermis are retinoid serums and hormone-containing serums such as estrogen and testosterone.

Which oils penetrate into the layers of the skin?

The depth of an oil’s penetration into the skin depends upon the type of fatty acid in the oil. Oleic acid is a monounsaturated fatty acid found in olive oil. It is the fatty acid that penetrates most into the skin. The use of olive oil and other oils with oleic acid can disrupt the skin barrier and lead to an increased risk of allergy and skin dehydration. Oleic acid is often added to topical drugs to increase skin penetration. One study [7] that compared the penetration of oils in the skin found that oleic acid penetrated the most, followed (in order of how much penetration the oil had) by coconut oil, grape seed oil, and avocado oil. Emu oil penetrated the least. Oils do not need to penetrate into the dermis to have beneficial effects. Stearic Acid, the fatty acid, is found in many cosmetic ingredients and oils and can help repair the skin barrier when combined with the correct amount of other lipids.

Which sunscreens penetrate into the skin?

Since there are many factors that can influence the penetration of sunscreen into the deep layers of the skin, each sunscreen must be tested individually. Chemical sunscreens are more likely to penetrate into deeper layers of the skin than mineral sunscreens do. One study compared different sunscreen ingredients and found that many chemical sunscreens only penetrate superficial layers of the skin, but benzophenone was able to penetrate to deeper layers. [8]

Physical mineral sunscreens that contain zinc oxide and titanium dioxide stay mainly on the surface of the skin and reflect away UV rays. This is one reason why mineral sunscreens look so white on the skin’s surface.

As you can see, there are many layers of the skin, and each plays an important role. The granular layer of the epidermis is a particularly interesting skin layer because the granules seen in this layer are little factories that are making lipids, keratin, filaggrin, loricrin and other building blocks of the skin. When these granular factories unload their contents into the cell or between cells, the granules disappear. This is why you do not see granules in the stratum corneum layer of the skin.

Although you do not need to understand all the layers of the skin to be a skincare expert, it is important to realize that the skin is designed to keep things out (except hormones), and most cosmetic ingredients just do not penetrate very deep in the skin. Penetration of skincare ingredients and the effects of combining ingredients on penetration are important considerations when developing a skincare regimen.

Optimizing the delivery of cosmeceutical ingredients to improve efficacy is the art and science of skincare routine design.

Take our quiz to find out which skin type you are and to get a skin care routine.

DQH Knowledge drop: In your 20s, your skin cell turnover decreases. (Cell turnover is a key component in keeping your skin youthful.) You know what else slows down? Your collagen production. Starting in your 20s, collagen decreases by about 1 percent per year. Should you want to prevent fine lines and wrinkles, start by eliminating behaviors that contribute to premature aging. “If it’s bad for you, it’s bad for your skin,” says dermatologist Michel Somenek. “Cigarette smoking reduces blood flow to the skin and causes premature wrinkling and a dull skin texture. Making the repeated pursed motion to inhale can also cause smoker’s lines. Alcohol and recreational drugs are toxins for the skin that damage its cellular structure and DNA,” Somenek tells us. “The faster you eliminate vices while you are young, the better chance your skin and body have to recuperate.” Also, adopting an anti-aging routine in your 20s is key. After all, the best offense is a good defense. We spoke to Somenek and experts Joshua Ross and Audrey Kunin to find out more. Keep reading for the best anti-aging products for your 20s, according to skincare professionals. Sunscreen “We all know that the sun is the number one cause of skin aging and starting the prevention in your 20s is very important,” Ross says. “The majority of your sun damage won’t start to appear until you’re in your 30s, so don’t wait until you see it surface or you’ll be behind the curve. Stay ahead of it with a good-quality zinc-based sunscreen worn daily.” Farmacy Green Defense Daily Mineral Sunscreen An invisible sunscreen with SPF 30, plus botanical extracts meant to protect skin with tons of antioxidants. Bonus: It’s clean and fine to use under makeup. Bareminerals Complexion Rescue™ Tinted Moisturizer Broad Spectrum SPF 30 Although we recommend you use your SPF and moisturizer separately, we also understand moments when you don’t have time or energy for that extra step. For those times, this bareMinerals moisturizer is a great thing to have on hand. Vitamin C Serum “A great introduction to anti-aging is to start with a vitamin C serum in your morning skincare routine,” Ross says. “It’s a powerful antioxidant that will neutralize free radicals and brighten the skin.” He adds that it’s a great way to counteract the effects of the sun’s harmful rays, which, as previously mentioned, are among the biggest causes of premature aging. Drunk Elephant C-Firma™ Vitamin C Day Serum The Drunk Elephant C-Firma is a lightweight serum that promises to give skin a glow by combining the brightening powers of vitamin C with ferulic acid, l-ascorbic acid, and vitamin E. The included sodium hyaluronate is meant to replace hydration loss, so you shouldn’t have to deal with any irritation. Sunday Riley C.E.O. Rapid Flash Brightening Serum This potent serum is jam-packed with vitamin C (15 percent, to be exact), which means it’s a potential superstar at both brightening skin and dousing it in antioxidants. Peptides Using peptides on your skin has many benefits, says Somenek. “The skin barrier is what defends the body against pollution, UV rays, bacteria, and toxins. It can be damaged by several everyday factors. Using topical peptides aids in building a stronger barrier,” he says. “Peptides comprise elastic fibers, which are a type of protein. These fibers help to make skin appear taut and firm. Peptides can also help repair damaged skin, relieve inflammation, and even out skin tone. Some peptides can kill acne-causing bacteria that is common in 20-somethings.” Kunin agrees, saying, “Peptides are an excellent entry point for supporting collagen.” She recommends looking for face and eye treatments that contain these collagen-boosting powerhouses. Charlotte Tilbury Magic Eye Rescue Cream This Charlotte Tilbury super-emollient eye cream has a base of coconut oil and shea butter (read: it’s incredibly hydrating). Botanicals plus peptides are meant to help reduce dark circles and boost collagen, respectively. This creamy moisturizer serves up potent collagen-boosting peptides and pycnogenol, and antioxidant-rich vitamin C. “Instead of sitting on top of the skin, peptides penetrate the outer layer so they go deep. The ‘signals’ they send tell the cells to produce elastin and collagen, which are needed for youthful-looking skin,” explains Somenek. At-Home Peel Pads Remember that skin cell turnover fiasco we talked about earlier? One way to help support it is by exfoliating. “Exfoliation is important to help keep skin fresh and luminous,” Kunin says. She recommends using at-home peel pads as an easy and effective way to exfoliate. “The goal in your 20s is to fight the slowing pace of cell turnover. It is wise to use products that gently exfoliate, yet still remove oil and other impurities. Products that have Alpha Hydroxy Acids (AHA) or Beta Hydroxy Acids (BHA) are a good choice.” According to Somenek, you should only exfoliate two to three times a week. “People of all ages are guilty of over-exfoliating and that can be too much of a good thing,” he says. Dermadoctor Kakadu C Intensive Vitamin C Peel Pad A few swipes of this Derma Doctor powerful peel pad promise to leave your skin glowing and smooth, thanks to the seven (yes, seven) types of chemical exfoliants, including AHA and BHA. It also contains vitamin C via Kakadu plum extract for added brightening and antioxidant protection. KEY INGREDIENTS Kakadu plum extract is sourced from the Kakadu plum, a fruit grown in northern Australia. It contains vitamin C, which restores the skin’s natural barrier, increases collagen production, and soothes irritation. Dr. Dennis Gross Skincare Alpha Beta® Universal Daily Peel Pads These are the gold standard of peel pads, with a cult following and over 900 five-star reviews on Sephora. They’re easy to use and contain a blend of anti-aging exfoliating acids. Emollient Night Cream “In your 20s, you need to start upping the hydration in your skincare routine. You may have been cautious of over-moisturizing because of acne in your teens, but as you enter your 20s, your skin transitions and becomes drier,” Ross says. “I recommend an emollient night cream added into your evening skincare regimen.” “Twenty-somethings need to make sure that they are not using creams that will clog their pores and cause excess oil production,” says Somenek. Opt for non-comedogenic products. Cerave Skin Renewing Night Cream One great choice is the CeraVe Skin Renewing Night Cream, which is a non-comedogenic night cream that leaves skin soft and glowy. It combines the moisturizing powers of ceramides and hyaluronic acid. RoC Retinol Correxion Max Hydration Creme “The best night cream ingredients contain retinol, benzoyl peroxide, and/or salicylic acid or hyaluronic acid. The goal is to moisturize, yet remove excess oil,” says Somenek. This Roc Retinol Correxion cream fits the bill as it contains both hyaluronic acid and retinol so it promises to moisturize while also being non-comedogenic.

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