Moisturisers, sunscreens and anti-ageing creams are usually sold on familiar promises: to keep water in the skin, strengthen its protective barrier, protect against sun damage or reduce visible signs of ageing. These functions remain central to healthy skin.

Researchers are now taking a broader view. The skin is also an active immune organ whose cells detect possible threats, send signals and help organise repairs. It is also home to communities of microbes that interact with the skin barrier and the immune system.

This shift could change what skincare products are designed to do, how companies test them and which claims regulators permit.

Skin cells can recognise germs, pollutants and signs of injury. They release signalling proteins that help coordinate inflammation and healing. A network of immune cells also detects potentially harmful substances, clears damaged cells and helps prevent immune reactions from continuing for too long.

Inflammation is essential when the skin is injured or infected. But immune reactions that are excessive or poorly controlled can contribute to irritation and disease.

Studies of acne suggest that inflammation may begin before spots become visible. Oil production, blocked hair follicles and Cutibacterium acnes bacteria remain important, but immune responses also influence how acne develops.

Rosacea involves inflammation alongside changes in........

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