Mignon Steele, of Wanganui Collegiate, asks :-

Why do we go pink when sunburnt? (Is it blood?)

Stewart Sinclair, a plastic surgeon who regularly works with burns victims, responded.

In a word, yes.

The skin pigment that colours black and brown skin is melanin - which protects its owners from sunburn. But people with pale skin have a relatively small amount of melanin and their skin is mostly coloured by the red pigment (haemoglobin) of the blood flowing through it. Further, the colour of blood can vary: blood loaded with oxygen is bright red; de-oxygenated blood is dark red.

The amount of blood flowing through the skin (in its capillary bed) is determined by the local blood vessel diameter, which can be affected by nerves and internal chemicals. If the feeding vessels (arterioles) are constricted the capillary bed will be relatively empty and the skin pale. If only the draining vessels (venules) are constricted then the capillary bed will be full of slow flowing de-oxygenated blood and the skin appears dark pink or bluish.

When the blood vessels are uniformly wide open, the skin is pink with lots of oxygenated blood. This is the situation when the skin is sunburnt (or injured in other ways, or infected):

there is a complicated reaction called the Inflammatory Response which releases chemicals that cause pain, swelling and dilatation of the blood vessels in the area of injury. Blood vessel dilatation means high blood flow, which you see as bright pink skin.