Sunscreen: how it works and how much to use

UVA and UVB are types of ultraviolet radiation that can damage skin and eyes, and health bodies say adults typically need about six to eight teaspoons of sunscreen to cover the whole body and should reapply every two hours.

Experts note many people do not use sunscreen correctly, and public health bodies have reiterated guidance about product choice and application. Ultraviolet A (UVA) and Ultraviolet B (UVB) are different wavelengths from the Sun that can help the body make vitamin D but also cause skin damage, premature ageing and increase the risk of skin cancer. Levels of UV vary during the day and are measured by the UV Index. Several UK health organizations and charities provide recommendations about SPF, UVA protection and application. What is known: - UVA and UVB are forms of ultraviolet radiation; both can harm skin and eyes and contribute to long-term skin damage. - The UV Index is a standard measure; Cancer Research reports that when the index is 3 or above people should use sunscreen and cover up. - SPF (sun protection factor) refers mainly to protection from UVB; the British Skin Foundation and NHS note that SPF 30 allows about 3% of UVB through and SPF 50 about 2%, and they recommend using at least SPF 30. - Star ratings on some products indicate UVA protection; the NHS recommends products with at least four stars and the letters "UVA" in a circle show compliance with EU standards. - The NHS says most people do not apply enough sunscreen and estimates adults covering their whole body need around six to eight teaspoons; it reports sunscreen should be applied ahead of sun exposure and reapplied about every two hours or sooner after sweating or water exposure. - The British Association of Dermatologists advises storing sunscreen in a cool, dry place; unopened products stored correctly typically last around 30 months, and a PAO symbol indicates how long a product remains effective after opening. Summary: Sunscreen can reduce exposure to harmful UV wavelengths but does not provide absolute protection, and effectiveness depends on product ratings and how much and how often it is applied. Public health guidance highlights choosing sufficiently high SPF and UVA-rated products, using an appropriate amount, reapplying as indicated, and following storage and expiry information.