Put very simply, the skin has both a functional and an aesthetic role. Functionally, it acts as a barrier separating the body from the external environment. It protects us from UV radiation and harmful substances, prevents excessive water loss, and helps regulate body temperature. It also produces vitamin D, which is essential for the proper functioning of cells throughout the body, and contains specialised sensory receptors that allow us to feel touch. From an aesthetic perspective, our skin reveals a great deal about our health, genetics, ancestry, age, and even the kind of work we have done throughout our lives.

The skin is often described as the largest organ in the human body, but there is another extremely important function I have not yet mentioned – its role in the immune system. Specialised cells found in the skin form an essential part of our immune defence. Much like in the gut, research has shown that these cells actively cooperate with the bacteria living on the skin’s surface.

It might actually be more accurate to say that the human body lives in a world of microorganisms. Bacteria, fungi, and viruses are virtually everywhere around us, and they are also an inseparable part of our bodies. For example, our gut contains an enormous number of microorganisms. Their influence on human health has been studied for decades, and in recent years we have become increasingly familiar with the term microbiome – the collective name for all the microorganisms living in a particular environment. We talk about the gut microbiome, the vaginal microbiome, or the skin microbiome. Within the microbiome, bacteria make up the bacteriome, viruses the virome, and fungi the mycobiome. It may sound like splitting hairs, but these terms sometimes help us better understand the subject. Even plant root systems have their own microbiome, and researchers have discovered that certain bacteria can influence plant growth and overall health.

It therefore comes as no surprise that our skin is colonised by microorganisms to varying degrees. Areas where the skin forms folds and where sweat and moisture accumulate contain larger numbers of bacteria, while places such as the upper arms or thighs tend to host fewer. We now know that the skin microbiome – especially its bacteria and yeasts – is essential and irreplaceable for healthy skin.

Now for the clinically most interesting part. The microbiome is remarkably stable, yet at the same time highly dynamic. In clinical practice, I often meet patients who say, “I’ve got Staphylococcus aureus, and it just keeps coming back.” But the truth is that most people carry this bacterium in their nose. The important question is whether it is a harmless strain, a more aggressive one, or whether the harmless strain has simply been given an opportunity to cause trouble. In the vast majority of cases, we coexist peacefully with the bacteria that make up our microbiome. Our immune system keeps them under control, and they maintain a friendly relationship with our body.

However, when unfamiliar bacteria reach our skin – for example through close contact with children, a new partner, or during a hospital stay – the risk of complications increases because these microorganisms are not adapted to our immune system. Fortunately, the bacteria that naturally belong to our skin microbiome help prevent these unfamiliar bacteria from settling on our skin in the first place.

There is an enormous amount that could be said about the microbiome – it is a fascinating area of research. One major limitation today is that we still cannot reliably test a person’s microbiome and clearly determine which one is “healthy” and which is not. What we can identify with confidence, however, is when certain medically significant bacteria become overgrown on the skin and are likely to be responsible for a skin condition.

Yes, it can, although the answer is a little more complex. The microbiome is a stable yet dynamic structure – its composition is influenced by our environment, habits, and the communities we come into contact with. Swimmers who spend time in chlorinated pools every day develop a differently stabilised skin microbiome from someone who only swims occasionally. The same principle applies to our skincare routine.

A complicated skincare routine is likely to alter the local composition of the skin microbiome to some extent, but I don’t believe this alone is necessarily harmful. Both the skin and its microbiome are capable of adapting to a demanding daily routine and finding a new balance. However, this adaptation always comes at a cost. The skin has to invest more energy into maintaining both its microbiome and its barrier function. Over time, this can leave it exhausted or more vulnerable to inflammation triggered by factors it would normally cope with. We commonly see this in flare-ups of atopic dermatitis, various forms of eczema, fungal infections, or impetigo.

There is another practical example that illustrates the relationship between the microbiome and skincare. A young woman came to see me with quite severe inflammatory lesions on her face. The condition, known as impetigo, is often caused by Staphylococcus aureus. It presents as weeping crusts and is highly contagious. We started treatment during her first appointment, and a week later everything seemed to be healing well. We assumed the problem had been resolved.

A few weeks later, however, she returned with exactly the same symptoms. This time we looked more closely at possible causes and discovered that she cleaned her face with a cosmetic flannel, which she stored in a damp container without washing or drying it properly. It had most likely become colonised by Staphylococcus aureus, and every time she washed her face, she was mechanically transferring the bacteria back onto her skin. The bacteria simply took advantage of the opportunity and caused the infection all over again.

I touched on the microbiome in my previous answer, but a damaged skin barrier is a broader concept. The skin itself also has a mechanical barrier function that protects us from the outside world. If external influences overwhelm its natural defences, damage occurs. One obvious example is a burn. The skin is designed to protect us from heat, but if the temperature is high enough, it simply cannot cope. At the other end of the spectrum are unsuitable cosmetic products used over a long period. They gradually exhaust the skin until it begins to respond with inflammation.

A classic example is perioral dermatitis. In children, it may develop because toothpaste is repeatedly left on the skin around the mouth after brushing their teeth. It can also occur after long-term use of moisturising creams. The skin typically becomes sensitive and red, small fluid-filled blisters may appear, and people often experience itching, burning, and mild flaking. Quite understandably, most people respond by trying another skincare product. Unfortunately, this often makes the condition worse or even leads to intolerance of additional products.

Sometimes the best approach is to do nothing at all. In dermatology, we call this a withdrawal strategy. We recommend using as few creams and active ingredients as possible, washing the face gently with cooled boiled water, and, if needed, applying cool compresses made from strong black tea. Then we simply allow the skin time to recover on its own – something healthy skin is perfectly capable of doing.

And once again, the microbiome plays an important role. When the skin barrier is weakened and exhausted, bacterial antigens penetrate the skin more easily, fuelling inflammation and making recovery more difficult.

Let me start with sunburn. Any sunburn, redness, or pigmentation caused by the sun is the skin’s response to UV radiation. Sunburn is a recognised risk factor for both non-melanoma skin cancers, such as basal cell carcinoma and squamous cell carcinoma, as well as melanoma. In fact, repeated sunburn – especially during childhood and adolescence – is considered one of the strongest proven risk factors for melanoma.

We also now know, and I hope dermatologists continue to spread this message, that sunscreen with SPF is not the only, or even the primary, form of protection against UV radiation, although it still plays a very important role. Despite the increased use of SPF products, the incidence of non-melanoma skin cancers continues to rise. One reason is that sunscreen often creates a false sense of security, while in reality it is rarely applied correctly.

So what is the right approach? The first line of defence is protective clothing and a hat. Sunscreen should then be applied generously to any skin that remains uncovered, such as the face, ears, hands, and legs, and it should be reapplied regularly throughout the day.

Take a look at tourists from many Asian countries, particularly South Korea. In many parts of Asia, fair, untanned skin is considered a symbol of beauty. Historically, this was probably because people with pale skin were those who could afford not to work outdoors in the fields or perform manual labour. Fair skin signalled wealth and social status. In Western culture, however, the perception has often been quite the opposite. A tan is frequently associated with holidays, leisure time, and an active outdoor lifestyle.

If you watch many Asian tourists, you’ll notice that they often wear loose long-sleeved clothing, arm covers or gloves, oversized sunglasses, and hats with very wide brims. It’s an interesting contrast in attitudes towards sun protection.

But what if the skin does get burnt? If it’s a typical sunburn with redness that later becomes itchy or painful, gels or lightweight creams containing panthenol provide excellent relief. A dermatologist may also prescribe preparations such as a light whipped cream formulation that can be stored in the fridge and applied several times a day as a cooling compress.

If blisters develop, the affected area should be gently dried rather than heavily moisturised. A simple and effective home remedy is a well-chilled, strong infusion of high-quality loose-leaf black tea. Once cooled, a thin film forms on the surface. After removing this film, the tannin-rich tea can be used as a cooling compress several times a day until the skin calms down. The rest of the treatment then follows much the same approach.

It’s important to remember that the skin “remembers” every single dose of UV radiation. That’s simply how biology and physics work. Over time, sun exposure leads to pigmentation changes, visible signs of skin ageing, and skin cancers, which are among the most common cancers worldwide. According to current evidence, sunburn itself – especially during childhood – is one of the key risk factors for both melanoma and non-melanoma skin cancers. Prevention really is the best protection, so it’s worth thinking about the long-term consequences.

If only the outermost layer of the skin, the epidermis, has been damaged, with no bleeding and at most a few thin fluid-filled blisters, recovery usually takes several weeks. People often quote around three weeks, but in reality it’s more likely to be closer to a month or even longer. Facial skin tends to heal slightly faster because the epidermis is thinner there. Even after healing, however, the affected area remains more sensitive to UV radiation for several months, and patches of lighter or darker pigmentation may develop.

When deeper layers of the skin are damaged, healing naturally takes longer. If crusts have formed, the initial healing phase still lasts several weeks, but complete recovery usually takes months. There is also a greater risk of permanent scarring due to remodelling of the deeper skin layers.

So when should you see a dermatologist or another doctor? If the affected area is extensive or involves high-risk locations such as the face, skin folds, or areas where skin rubs together, medical assessment is advisable. You should also seek medical attention if redness and swelling spread around the damaged skin or if you develop general symptoms such as a fever, chills, or shivering. In these situations, it’s best to seek medical care without delay.

Burns deserve a special mention. In dermatology, we don’t encounter them as frequently because they are often managed by highly experienced dermatologists or plastic surgeons. But one piece of advice from my own clinical practice is this: if you sustain a burn, even one covering only a few square centimetres, or any burn involving the face, see a doctor immediately.

Burns are unpredictable. People often assume that what looks like simple redness will heal on its own, but that’s not always the case. Just a few days ago, a mother brought in her teenage daughter with a burn roughly the size of a large coin near the corner of her mouth. A week earlier, she had been roasting marshmallows with friends when a piece of hot marshmallow stuck to her face. They treated the burn at home for a week before seeking medical advice. By then, the tissue had become necrotic and the burn had deepened significantly. Sadly, she will most likely be left with a permanent facial scar.

Prevention, common sense, and never underestimating burns – those are the most important lessons I can share from clinical practice.