Key points
- Skin is the body's largest organ: it protects against germs and water loss, helps control temperature, senses touch, heat and cold, and makes vitamin D from sunlight (NIH; WHO, 21 June 2022).
- Acne, eczema, rosacea and hives are the skin conditions people ask about most — each is named here in plain language, with no prevalence figure claimed (no verified global figure exists for them as single conditions).
- Eczema is not contagious. Skin conditions are not a sign of poor hygiene, and they are not caught from another person by touch.
- Skin changes with age: it becomes thinner and drier, and dry skin is common in older age. Sun protection matters at every age — see the sun and skin guide.
Direct answer: Skin is the body's largest organ and its first line of defence: it keeps germs out, holds water in, helps control temperature, senses touch, heat and cold, and makes vitamin D from sunlight. This page names the skin conditions people ask about most — acne, eczema, rosacea and hives — in plain language, explains how skin changes with age, and says where to read more. It does not diagnose anything, and it does not say what any spot or rash means for an individual.
What your skin does
Skin does more than cover the body. It is a barrier: it keeps germs out and stops the body losing too much water. It helps control temperature, through sweating and through blood flow near the surface. It is full of nerve endings, so it senses touch, heat and cold. And small amounts of ultraviolet light on skin produce vitamin D, which the body needs — while too much of the same light damages skin and can cause skin cancer (WHO, “Ultraviolet radiation” fact sheet, published 21 June 2022).
Skin has three layers: the outer epidermis, the dermis beneath it, and the fatty subcutaneous layer below that. The epidermis is constantly renewing itself, shedding old cells as new ones rise to the surface. That renewal is why skin can recover from everyday wear, and why its condition reflects both age and environment.
Acne
Acne is one of the most commonly asked-about skin conditions, and it is most common in teenagers — the age when skin produces more oil. It is named here because people ask about it, not because this page can say anything about any individual’s skin. Acne is a skin condition, not a sign of poor hygiene, and it is not contagious. For detail about acne itself, the NHS Conditions A to Z pages are the plain-language reference this site links to rather than repeating.
Eczema
Eczema is a group of conditions in which skin becomes dry, itchy and irritated. The fact people most often ask about is also the simplest: eczema is not contagious. It cannot be caught from another person by touch, and it is not caused by poor hygiene. Eczema is common in children and can continue into adult life; how common it is worldwide as a single figure is not something this site states, because no verified global figure for eczema alone was confirmed in the research behind this page.
Rosacea
Rosacea is a long-term skin condition that mainly affects the face. It is named here because it is one of the conditions people ask about most, alongside acne and eczema. Like the other conditions on this page, it is described at population level only: this page names it, says it is a recognised skin condition rather than a passing rash, and points to the NHS Conditions A to Z pages for detail. It does not describe what any individual’s redness or spots mean.
Hives
Hives are raised, itchy welts on the skin that come and go. They are named here for the same reason as the other conditions on this page: people ask about them, and a plain-language awareness page should name them rather than leave them out. Hives are a skin reaction, not an infection, and they are not caught from another person. Beyond that, this page does not go into causes for any individual case — that is a question for a clinician.
Skin in older age
Skin changes with age. It becomes thinner and drier, and dry skin is common in older age — the subject of NHS skin-care guidance for older people. Older skin is also more easily damaged by the sun, and a lifetime of sun exposure adds up: the WHO fact sheet notes that chronic sun effects include premature skin ageing as well as skin cancers. None of this is a reason for alarm; it is a reason the same basic care — washing, moisturising as needed, and sun protection — matters at every age, and more so as skin thins.
Looking after your skin
There is no single routine this site prescribes, because skin care is personal and this site gives no personal advice. The population-level points are simple. Keep skin clean with ordinary washing. Protect it from the sun: the WHO measures are shade in the middle of the day, protective clothing, a broad-brimmed hat, wraparound sunglasses, and broad-spectrum sunscreen on uncovered skin — with shade and clothing first, and sunscreen not used as a way to stay in the sun longer. Those measures are described in full in the companion guide on sun and skin, which also links to the UV Index Lookup tool. And for any personal question — a new growth, a sore that does not heal, or a change in a mole — the awareness-level advice is to see a clinician.
Frequently asked questions
What does skin do for the body?
It protects the body from germs and water loss, helps control temperature, senses touch, heat and cold, and makes vitamin D from sunlight.
Is eczema contagious?
No. Eczema is not contagious — it cannot be caught from another person by touch.
Does this page say what a spot or rash means?
No. It names conditions at population level only. For a personal question about your own skin, see a clinician.