Hormonal changes, usually in teenagers, generate more oily secretions that block up skin pores. These then become infected. A diet high in saturated fat and fried food will have a similar effect. Vitamin A and zinc deficiency leads to a lowered ability to fight infection. So it' s sensible to eat a healthy diet of wholefoods; avoid fatty meats, too much cheese and fried foods; and have plenty of fruit and vegetables, as well as 1.5 litres of pure water a day.

Supplementing 20mg of zinc and up to 5,000mcg of vitamin A can help, but limit the A to 3,000mcg if you' re pregnant.