As we enter the height of summer, the warmer, sunnier weather takes its toll on our bodies. This includes minor irritants, such as sweatier armpits, as well as major risks, such as heat stroke or severe sunburn.

Some even believe that summer can help your hair grow faster. The scientific evidence behind this idea is more of a patchy blend than a thick mane. But there are some reasons to think that summer, and specifically the sun, could help hair growth.

What is the hair growth cycle?

One thing is clear: our hair does not always grow at the same rate.

On average, our scalp adds about five inches of hair each year. Our hair follicles go through four phases: growth (anagen), transition (catagen), rest (telogen) and shedding (exogenous). The individual hair follicles on our scalp remain in the growth phase for between two and eight years on their own independent schedules, but this duration shortens as we age, producing thinner, weaker hair.

Factors like genetics, nutrition, medications, stress, and inflammation influence the hair cycle, says board-certified dermatologist Elizabeth Bahar Houshmand, based in Dallas, Texas. popular science.

“For example, thyroid disease, iron deficiency, a major illness, surgery, rapid weight loss, postpartum hormonal changes, and certain medications can cause more hairs to enter the shedding phase, leading to more hair loss several months later,” Houshmand says.

Does hair grow more in summer?

The idea that hair grows differently in summer is popular, says Houshmand. “There may be some biological plausibility because exposure to light, temperature, circulation, and seasonal hormonal changes can affect many physiological processes,” he adds.

Environmental factors, such as pollutants, can also affect the scalp barrier and inflammation. Houshmand says this can contribute to optimal hair growth. But she says seasonal factors, such as the summer sun, are unlikely to have a significant effect on our hair growth. “In dermatology, we typically think of hair growth as being driven internally by follicle biology, health status, and signaling pathways,” Houshmand says.

Increased vitamin D production thanks to more sunlight is often touted as the reason hair is thought to grow faster in summer. But Houshmand quickly dismissed this idea.

“If someone has a true vitamin D deficiency, correcting that deficiency can support overall health and can be part of a broader hair loss treatment plan. But there is no strong evidence that taking extra vitamin D will make hair grow faster in someone with normal vitamin D levels,” he says. In other words, excess vitamin D is probably not the cause of luscious hair.

The idea that the sun and summer influence hair growth at all has not been scientifically proven, explains Houshmand. Only a few studies have addressed the issue and they do little to obscure the theory’s weaknesses.

Two studies conducted in the 1990s explored seasonal changes in hair growth in men. An article, published in British Journal of Dermatology In 1991, they found that their participants’ scalp hair was most commonly in anagen in March, where 90 percent of the follicles were in the growth phase. This ratio then fell over the next six months, reaching a low in September. The participants’ beard hair grew differently and peaked in summer. In July, beard growth was 60 percent higher than winter levels.

The second study, which appeared in the same journal five years later, concluded something similar: the end of summer marked the time of year when the greatest number of hairs were in the resting phase of growth. Taken together, this evidence suggests that summer is when hair is likely to grow less, rather than longer. But both studies were very small, with only 14 and 10 participants respectively, making it difficult to generalize the findings to the broader population.

A more recent study was published in the journal Dermatology in 2009. It was much larger and recruited 823 women. The cohort included both healthy participants and those suffering from clinical alopecia, a condition characterized by rapid hair loss. Once again, this showed that summer was the time of year when most follicles were in the telogen resting phase.

Even if beard hair grew 60 percent faster in summer, this would only translate to 0.3 inches more growth than normal in a month, which is not enough to notice.

Don’t forget that sun exposure, when done safely, has positive effects on our body, such as increasing the production of the hormone serotonin, which improves mood. But the idea that moving to a sunnier climate could fix receding hairline isn’t thick enough to run a comb through.

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