Most of the time, the immune system sounds like an invisible power working behind the scenes, keeping you safe and healthy without you having to think too hard about it (flu season notwithstanding). And to some extent, that’s true. But the immune system is way more sophisticated than you might think, and it’s definitely not invisible. In fact, your skin — the body’s largest (and most visible!) organ — accounts for a huge part of it.

Think of your skin as the first line of defense to the world. It protects your entire body from foreign aggressors, be they pollution or bacteria, which is why the common areas of vulnerability (like the eyes, nose, and mouth) tend to have a mucous membrane instead of the usual layers of skin found everywhere else. And skin’s pretty good at its job. For instance, the average cold virus can’t enter your body through your arm.

Here, we’re getting into the ins and outs of the skin’s immune system and why it’s so important to keep it healthy.

What Is the Skin Immune System?

Your skin’s immune system is made of several different barriers, which all work as a team to keep foreign invaders at bay. First, there’s the physical skin barrier. “The physical skin barrier refers to the individual skin cells known as keratinocytes that serve as a physical barrier,” says Marisa Garshick, MD, a dermatologist in New York City. “It’s often considered a line of defense against external stressors and pathogens, preventing entry of unwanted factors.”

Skin also has a moisture barrier, with which the skin-care obsessed may already be very familiar. “It uses fatty molecules to prevent water loss and keep moisture in, keeping the skin hydrated,” explains Garshick.

While the physical barrier gets all the love, there’s also a chemical barrier, also known as the acid mantle. That’s in charge of your skin’s pH. “It keeps the skin at a slightly acidic pH, keeping the barrier function intact,” explains Garshick. “If the acid mantle is disrupted, it can make the skin more susceptible to other injury and further disruption of the skin’s microbiome.”

Speaking of, there’s the microbiome, which refers to “the microorganisms that live on the skin and comprise the skin flora — which can actually be helpful to protect the skin, help boost immunity, keep pH in balance, and more,” says Garshick. Calm, balanced skin means that the good bacteria are keeping the harmful bacteria on your skin in check. 

Last but definitely not least, you have an immune barrier. It includes immune-system cells that serve as your body’s scouts. “They are designed to sense changes to the skin or body, recognize certain things as foreign, and trigger the immune system to help to protect against certain pathogens as well as to form memory to be able to fight against infection,” says Garshick.

How the Skin Immunity Works

Your skin’s immune system is a localized version of your overall immune system. And it’s not tasked with dealing with just outsiders. “Skin immunity is in place to help to protect the body from infection, but also from cancer and other factors that may be considered foreign to the body,” Garshick says.

Through a complex system, it raises the alarm bells when something seems off. “Skin immunity includes different types of immune responses depending on the exposure type, with certain cells being activated in certain conditions or with certain exposures,” says Garshick. “Similarly, certain immune cells are present in the upper and deeper layers of the skin which may have different functions, but together trigger an inflammatory reaction.”

That inflammation tells your body that something’s up; it can manifest as redness, swelling, or itchiness. “By triggering an inflammatory reaction, skin immunity can allow the body to fight off the pathogen,” Garshick says. It also creates a sort of record of the inflammatory event when it happens for your body to reference in case it occurs again. “When the adaptive immune response is utilized, it refers to a response that is specific to a certain pathogen and creates memory to allow the body to fight off the pathogen upon re-exposure,” says Garshick.

Skin inflammation comes up a lot around here, because it’s a complicated topic. On one hand, it’s essential for tissue repair and regeneration in addition to flagging down your immune system. (In fact, it can even help promote collagen growth.)

Read all about Skin Inflammation: The Good, the Bad, and Everything in Between

That said, inflammation can go haywire or become chronic. “Often the inflammatory reaction is designed to help protect the skin and the body, but in certain conditions the immune system can be upregulated or go into overdrive, such as in atopic dermatitis, which can lead to red, flaky skin,” says Garshick. Other forms of immune system dysfunction in the skin manifest as psoriasis or allergies.

How to Boost Your Skin’s Immune System

Like so much in skincare, it all comes down to your skin barrier. “Anything that’s done to help protect the skin barrier can effectively help with skin immunity — whereas when the skin barrier is compromised, it leaves the skin more susceptible to irritation and sensitivity,” explains Garshick. A good example? Maskne, in which friction from the mask and heat trapped within lead to a compromised barrier and, of course, acne. Anything that impairs your skin barrier, be it overcleansing or harsh exfoliants, can thus leave your skin immune system more vulnerable.

On the other hand, barrier-supporting ingredients throughout your skin-care routine can help, from camellia and apricot kernel seed oils in the Papaya Sorbet Enzyme Cleansing Balm to avocado oil in the Avocado Melt Retinol Sleeping Mask. They help replenish the lipids in the moisture barrier, fortifying it and keeping it intact.

Magnesium in the Banana Soufflé Moisture Cream also helps maintain barrier health and calm inflamed or stressed-out skin. Also, says Garshick, “antioxidants can be utilized to help to protect the skin from free radical damage which can impact skin cells and skin cell function.” The Pineapple-C Bright Serum is brimming with vitamin C, one of nature’s most powerful antioxidants, while the three plums in the Plum Plump Hyaluronic Serum are rich in antioxidants — kakadu plum contains 100 times the amount of vitamin C found in an orange.

Finally, the immune system in general also gets a boost when you maintain a healthy lifestyle and diet — think regular physical activity and fruits and vegetables. Since it’s in charge of keeping you safe, it’s worth doing what you can to keep it healthy, happy, and strong — even if that means breaking a sweat in addition to slathering on serum.

Read more about keeping skin healthy and calm:

• Is Your Skin Barrier Broken? Here’s What to Do
• Skin Inflammation: The Good, the Bad, & Everything in Between
• Skin Redness? Here’s What Might Be Causing It