Functions of the skin
Skin is your body's outer cover. Its jobs are: protect against germs, dust, water loss and sunlight; sense touch, pain, heat and cold; control temperature; remove a little waste in sweat; and make vitamin D.
Parts of the skin and how they match their jobs
Epidermis is thin and tough. Dead cells on top form a waterproof shield. Cells at the bottom make melanin, a brown pigment that absorbs UV.
Dermis is thick. It has blood vessels (food and heat), nerves (touch and pain), sweat glands, oil glands and hair roots. Oil keeps hair and skin soft.
Fat layer stores energy, cushions and keeps heat in.
Skin and thermoregulation
Your body stays near 37 °C. When you are hot, vessels in the dermis widen so more warm blood is near the surface, and sweat glands release sweat. Sweat takes heat with it as it evaporates. When you are cold, vessels narrow to save heat, hairs stand up (goosebumps) and you may shiver.
Provitamin D synthesis
A form of cholesterol in the skin, called provitamin D, changes into vitamin D when UV-B light hits it. Vitamin D helps the body take calcium for strong bones. Ten to twenty minutes of morning or late-afternoon sun on arms and face is usually enough, so long shifts in strong sun are not needed.
UV, skin ageing and skin disease risk
UV light can damage the DNA in skin cells. Short-term it causes sunburn. Over years it causes wrinkles and dry, spotted skin (photo-ageing) and raises the risk of skin cancer. Protect yourself: shade between 11 am and 3 pm, cap, long sleeves, sunglasses and sunscreen (SPF 30+).
When a skin change needs a doctor
See a doctor if a mole grows, changes colour or shape, has uneven edges, itches or bleeds; if a sore does not heal in a few weeks; if a rash spreads, hurts or comes with fever; or if a cut looks red, swollen and pus-filled.
Skin diseases: fungal infections, melanoma and prevention
Fungal infections (like ringworm or athlete's foot) grow in warm, damp places. They cause round, itchy patches. Prevent them by keeping skin dry, not sharing towels or combs and wearing clean cotton clothes. A doctor gives antifungal medicine.
Melanoma is a serious skin cancer that starts in melanin cells, often as a changing dark mole. It spreads if found late, but is usually curable when found early. Prevention: avoid sunburn, use sun cover, and check moles regularly.
Try it
In the 3D, move the heat slider from cold to hot and say what happens to the vessel, the hairs and the sweat. Move the UV slider and count the melanin dots. At home: look at your palm skin after a hot run, and look for the pink colour of widened vessels. Never stare at the sun; just notice the shadow.
Key formulas and definitions
- Layers: Epidermis (top), Dermis (middle), Fat layer (bottom)
- Hot: vessels widen + sweat out. Cold: vessels narrow + hairs rise
- UV-B + skin provitamin D = vitamin D
- More UV = more melanin; too much UV = DNA damage
Worked examples
1. Why do your cheeks turn red after running?
Running makes heat. Blood vessels in the dermis widen to bring warm blood close to the surface so the heat can leave. More blood near the surface shows as red.
2. A mole has grown larger and has uneven edges. What should you do?
Show it to a doctor soon. Changing size, colour or edges are warning signs of melanoma, which is easier to treat when found early.
3. Why can a short walk in morning sun help the bones?
UV-B light turns provitamin D in the skin into vitamin D, which helps the body absorb calcium for bones.
Common mistakes
- Thinking sweat itself cools the body. It cools when it evaporates.
- Saying a tan is healthy. A tan means the skin is already protecting itself from UV damage.
- Thinking vitamin D needs hours in the sun. A short, safe time is enough.
- Using the same towel or comb with someone who has a fungal infection.