Skin and hair

Skin and hair are the most visible parts of the body to change with age. Most of the change is set by age and inheritance, but some is driven by external exposures, above all ultraviolet (UV) radiation from sunlight, and some of it reflects or accompanies the health of other organs. The same UV exposure that ages the skin causes most skin cancers: in 2020 more than 1.5 million skin cancers were diagnosed worldwide, with more than 120,000 associated deaths [1].

Skin aging describes wrinkling, sagging and loss of elasticity, and the difference between intrinsic aging (driven by age and genes) and sun-driven photoaging. In a randomised trial (a study that assigns participants to groups by chance) in Australia, adults assigned to daily sunscreen showed no detectable increase in skin aging over 4.5 years [2]. How old a person looks is associated with survival: among 1,826 Danish twins aged 70 or over, the twin who looked older in photographs was more likely to die first [3]. The article also covers under-eye bags, which are mostly inherited anatomy; sagging of the upper eyelids was estimated to be 61% heritable (explained by genes) in British twins [4].

Hair loss describes pattern baldness and other forms of alopecia (the medical term for hair loss). Pattern hair loss affects 30 to 50% of men by age 50, and heredity accounts for about 80% of the predisposition [5]. It does not shorten life directly, but severe baldness on the crown was associated with 32% higher risk of coronary heart disease (narrowing of the arteries that supply the heart) in pooled studies of about 37,000 men [6], and melanoma (the most dangerous skin cancer) of the scalp or neck carries a higher rate of death than melanoma of the arms and legs [7]. Most of this evidence is observational, from tracking people rather than assigning them to an exposure, so it identifies markers of risk more reliably than causes.