How heat, humidity affect human skin?

Global warming and extreme heat are increasingly affecting human health. In relevant studies, environmental temperature and relative humidity are summed up as a heat index because they influence and increase each other. As the heat index increases, the risk of developing various diseases—such as cardiovascular and pulmonary—also increases.

Although the skin is an organ in direct contact with the environment, it is currently unknown whether this also affects skin health.

Mechanistic studies have shown that heat affects biological processes that may contribute to skin aging.

A new paper published in the journal Dermatitis is the first epidemiological study to examine the relationship between heat index and skin aging. India, with its diverse climate zones and higher temperatures compared to its latitudes, is particularly suitable for such studies. In the study, signs of skin aging—such as age spots and wrinkles—were assessed among 1,510 Indian women from three different cities—and using the SCINEXA scoring system.

In addition, ambient temperature and relative humidity data were collected over the past five years in the respective residential areas and combined into a heat index, along with data on UV radiation and air pollution.

To calculate the statistical relationship—so-called association—between the heat index and signs of skin aging, a fitted multivariate logistic regression model was used.

The study showed that forehead pigmentation and deep wrinkles—such as crow's feet and under-eye wrinkles—also increased considerably with increasing heat index.

Furthermore, these associations were found to be independent of the age of the participants and other environmental factors such as UV exposure, smoking, and air pollution.