What is the largest organ of the human body?

The skin, at roughly two square metres and around 16 per cent of body weight. Calling it an organ rather than a wrapper is the right way round: it regulates temperature, manufactures vitamin D, keeps water in and pathogens out, and is the largest sensory surface you have.

It replaces itself constantly. The outer layer is made of dead, flattened, keratin-filled cells that are continuously shed - a good fraction of household dust is skin - and the whole epidermis turns over in about a month. Below that sits a layer of collagen and elastin which does not renew nearly as well, which is essentially what ageing skin is.

Two common claims deserve trimming. It is often called the largest by area, which is only true if you ignore the lungs and the gut, whose folded surfaces are vastly larger. And melanin, the pigment that colours it, is doing a specific job: absorbing ultraviolet before it reaches the DNA underneath.