Do humans have a shedding season? According to an analysis of Google searches for "hair loss," that may be the case: A new study finds that these searches spike in the summer and fall.
Hair loss searches were greatest in the summer in both hemispheres of the globe, followed closely by the number of searches in the fall, according to the study, published yesterday (Oct. 24) in the British Journal of Dermatology. The searches for hair loss reached a low during the spring.
Though Google searches for hair loss do not necessarily mean that the person who did the search has hair loss, the findings "back up the results of smaller studies involving patients that showed greater [hair loss] in the summer months," said senior study author Dr. Shawn Kwatra, an assistant professor of dermatology at Johns Hopkins University School of Medicine. [The 7 Biggest Mysteries of the Human Body]
Ultimately, the findings suggest that people "can expect to have more [hair loss] in the fall and summer," Kwatra told Live Science.
The researchers looked at data from 2004 to 2016 from eight countries around the world, covering both the northern and southern hemispheres: the United States, the United Kingdom, India, Canada, Australia, South Africa, New Zealand and Mauritius (an island in the Indian Ocean). To avoid any ambiguity in the search analysis, the researchers included only English-speaking countries.
For countries in the Northern Hemisphere, the researchers defined spring as March, April and May; summer as June, July and August; fall as September, October and November; and winter as December, January and February. In the Southern Hemisphere countries, the seasons were the opposite, such that the northern spring was the southern fall and the northern summer was the southern winter, and so on.
Previous studies have suggested that there may be a link between seasonality and hair loss, the researchers wrote. For example, earlier research has shown that people have the highest rates of "telogen" hairs in the summer, and the lowest rates of these hairs in the winter. Telogen hairs refers to hairs in their final stage of growth. (There are three stages of hair growth.) Hairs in the telogen stage are most likely to fall out.
Monthly temperature data for the eight countries were obtained from the National Oceanic and Atmospheric Administration.
Though "temperature was associated with hair loss, there are likely other factors, such as UV index, that may help to explain the relationship between seasonality and hair loss," Kwatra said. The UV index refers to the strength of ultraviolet rays outdoors; it's possible that UV rays could influence hair loss, according to the study.
Originally published on Live Science.