The grease that appears on our hair and scalp is a combination things. “It’s mainly sebum – an oily substance produced by sebaceous glands,” says Kingsley. “The main components of this are fat and cellular debris. However, this ‘grease’ will also consist of sweat, dead skin cells and environmental pollution.”

Whenever hormone levels change, scalp secretions can change too. “The scalp usually becomes oilier during puberty, in times of intense stress and also during ovulation,” she explains. “Medical conditions such as Polycystic Ovarian Syndrome (PCOS) can also cause an overly oily scalp. After menopause, sebaceous glands on the scalp tend to produce less sebum.”

People with naturally fine hair may find that their hair gets greasy faster than those with other hair textures. “This is because individuals with fine hair have more hairs per square centimetre – and each hair has a sebaceous (oil) gland attached to it,” says Kingsley. “As a result, the scalp produces more oils.”

Our environment can have a big impact too, even if we’re just sitting at home. “Pollution affects the hair and scalp in a similar way to the skin on our face,” says Kingsley. “It makes our hair and scalp dirty and can also increase the likelihood of scalp problems, such as flaking and itching, as well as the formation of pimples.”

“In terms of your hair, pollution can make it look dull and lacklustre, and feel coated and heavy,” she adds. “The hair at the back of the head has a tendency to get oilier as this is the area that we tend to sleep on and rest our head on. It therefore becomes warmer than other parts of the scalp and sweats more. An increase in temperature and sweating stimulates the sebaceous glands.”

What causes greasy hair and how to stop it