How Your Skin Protects Itself

How Your Skin Protects Itself

It’s just crazy when you think about how much is going on in/on your skin to protect you at any given moment! 

One of the main purposes of your skin is to protect your body from things that can harm it like pollutants, irritants, and pathogens.

Here are the 4 ways your skin protects itself…


Pathogens = bad bacteria that want to damage your cells and cause infections.

Healthy skin makes it very hard for pathogens to get in.

I’m going to share a post I made for my Instagram account @sciencebecomesher here because I think it illustrates how hard it actually is for a pathogen to get into your skin…

Pathogens vs Your Skin

Imagine you’re a naughty little pathogen…

 In order to pass through the epidermis, you’ve got to make it through 4 different protective barriers:

1. First – the skin microbiome – a community of millions of different microorganisms that live on the surface of the skin. When these microorganisms are unbalanced (bad bacteria outnumbers good bacteria) you (the pathogen) are able to grow and multiply ready for invasion.

2. Next, the acid mantle – a protective film made up of sweat, sebum, and lactic acid that keeps your skin at a naturally acidic pH. You (the pathogen) thrive at a more neutral pH so, if skin pH is higher (e.g. from using the wrong skincare products or overdoing it) you’re loving life.

3. Then you have to content with a physical barrier – the stratum corneum (swipe for this). It’s usually pretty hard to penetrate the stratum corneum but if you (the pathogen) are particularly lucky, the skin has been stripped of it’s natural lipids (e.g. from overexfoliating) and there are little gaps that you can squeeze on through.

4. Finally – you have to take on the skin’s immune system. In the epidermis, Langerhans cells are the main immune cells. They’re probably going to kill you (by alerting the immune system to your presence) but at least you’ve had a chance to cause some inflammation and irritation.

Aaaaaaaaaaaannd, you’re back in the room!

Now you know all the barriers pathogens have to pass through in order to cause irritation, inflammation, and infection. I’ll go into a little bit more detail on each of the 4 ways your skin protects itself and what you can do to keep your skin fighting fit!

The 4 Ways Your Skin Protects Itself

So, as mentioned above, the 4 ways your skin protects itself (its various protective barriers) include:

  • Your skin microbiome
  • Your acid mantle
  • Your stratum corneum (physical barrier)
  • Your skin’s immune system (mainly Langerhans cells)

The Skin Microbiome

Your skin microbiome (or normal flora) is a community of millions of different microorganisms that live on the surface of your skin that help keep your skin healthy. 

It’s mainly made up of bacteria, fungi, viruses, and mites.  

Sounds awful right? Like when you see microscopic pictures of those little eyelash mites and then convince yourself you can feel them moving.

There’s no need to worry though, although it may not sound like it, these microbes are very beneficial to your skin.

In fact, they’re pretty essential to keeping your skin healthy – as long as they are balanced.

Balanced microbiome = hard for pathogens to get in

(a bit like how having a fence around your house makes it a little harder, but not impossible, for burglars to get in)

Your skin microbiome works in partnership with your skin’s immune cells by programming the immune cells to respond to any pathogens that do manage to get into your skin.

What Happens When Your Skin Microbiome Is Unbalanced

An unbalanced microbiome (dysbiosis) means that you have less beneficial bacteria on your skin and an increase in bad bacteria and/or good bacteria that can become bad bacteria under certain conditions. 

For example, some of the key bacteria that make up your skin microbiome, particularly C.acnes and S.epidermidis, help protect your skin when they are balanced. However, they can easily shift into ‘opportunistic pathogens’ when they are not.

Some skin conditions are also associated with an imbalance of these bacteria:

  • Atopic dermatitis (eczema) is associated with an increase in S.aureus (as well as an increase in S. epidermidis during flares) and a decrease in C. acnes and lactobacilli.
  • A decrease in C. acnes and lactobacilli has also been found in psoriasis.
  • An increase in C. acnes is one of the key characteristics of acne.

Your skin microbiome is heavily influenced by your acid mantle.

Your Acid Mantle

The pH of your skin is naturally acidic (pH 4.7 – 5.9) and controlled by a mixture of sebum, sweat, lactic acid, and fatty acids that create a film-like covering on the surface of your skin known as your acid mantle.

It’s important to keep your skin pH in this range as it allows your good bacteria to thrive while limiting the growth of bad bacteria which prefer a more alkaline pH (above 7.0).

If your skin pH is elevated, these bad bacteria multiply and outnumber your good bacteria which results in an unbalanced microbiome. 

Not only does this increase your risk of skin infection from the bacteria present in your environment but it also alters the behavior of your good bacteria.

Back to the burglar analogy – think of your acid mantle as an outside security system/guard dog – the burglar has managed to climb over your fence (your microbiome) and has now come face to face with your guard dog, except you forgot to feed your dog, and the burglar has some yummy dog treats…

There are a number of things that can throw your skin’s microbiome off balance, including:

  • Sun damage
  • Skincare products
  • Antibiotic treatments
  • Pollution
  • Diet
  • Over-exfoliation

Your Skin Barrier

Your skin barrier (a.k.a. Your stratum corneum) has a ‘brick-and-mortar’ like structure where your skin cells (the bricks) are held together by a glue-like mixture of lipids (mortar). These lipids are made up of a mixture of ceramides, cholesterol, and fatty acids and work together to create a physical barrier that prevents water from escaping your skin and irritants from entering.

Healthy skin barrier = pathogens find it hard to get in

Think about that burglar again, they’ve made it over your fence, past your hungry guard dog (who is now their best friend because… treats are life), and now they’re at your front door. Except, you’ve got one of those super strong doors that’s really hard to break into…

However, when your skin barrier is stripped of lipids and is damaged/compromised, the pathogen can make its way through the little gaps that have formed. Darn it, you forgot to lock your door! This burglar is having the best luck ever…This activates your skin’s immune system which causes inflammation and irritation. It also means that water can escape through the gaps and leave you with dry and dehydrated skin.

Things that can damage your skin barrier include:

  • Over-exfoliating and using skincare products and ingredients that are stripping/drying
  • Sun damage
  • Pollution and environmental stressors (cold weather, hot showers, etc.)


Your Skin’s Immune System

Your skin has it’s own little ‘immune system’ of cells and molecules that protect your body from any pathogens that get through your skin barrier.

They include:

  • Langerhans cells
  • T Cells
  • B Cells
  • Natural Killer Cells

Langerhans cells are quite possibly one of the most important parts of your skin’s immune system as they help your body work out which substances are harmful and which aren’t.

Like whether it’s a burglar trying to get in your house or just your drunk Aunt Shirley who forgot her keys.

When Langerhans cells misidentify a substance as harmful (e.g. a new skincare product) it can lead to an allergic reaction.

If the substance is identified as harmful (rightly or wrongly), T cells (a type of white blood cell) are activated and sent to the area where the suspected pathogen was found.

Side note: if you’ve ever squeezed a spot and seen that clearish/yellow fluid – that’s full of white blood cells – and pus, the yellowish/white stuff is dead blood cells (when they’re done killing bacteria) 

So, basically, you tazer the burglar and the threat to your health is now neutralized, but you’re still a little shaken up.

Plus, on the odd occasion you might accidentally taser Aunt Shirley and now the rest of your family is mad at you (except Uncle John, who found it funny).

This is a bit like what’s happening in your skin. In most cases, your immune system is going to neutralise the pathogen trying to invade your body (unless you’re immunocompromised), but you’re still going to experience inflammation and irritation – which isn’t ideal and is going to worsen skin conditions like acne, rosacea, and eczema.

The best way to avoid this, is by keeping your skin’s protective systems healthy so that the pathogen never makes it into your skin in the first place.

Build a taller fence

Maintain your security systems/ feed your guard dog

Lock your door

In other words:

Those are the 4 ways your skin protects itself.

Thank you for reading! 

This article of the Skinsider Scoop was graciously written by Content Creator/Skincare Educator, Laura Hayes and edited by the Clean Skin Club team. If you're interested in more from Laura, follow her Instagram @sciencebecomesher