Hair grows in a natural cycle that includes periods of growth, rest, and shedding.
How quickly hair grows depends primarily on genetics, diet, illness, and hormones.
That is according to dermatologist Elizabeth Bahar Houshmand, speaking to Popular Science.
She also explains that factors such as iron deficiency, illness, and stress can lead to increased hair loss.
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The sun is not the solution
Many people believe that more sunlight and higher temperatures make hair grow faster.
According to Popular Science, however, there is only limited research supporting that theory.
Although sunlight increases the body's production of vitamin D, there is no strong evidence that additional vitamin D leads to faster hair growth in people with normal vitamin D levels.
Hair growth is primarily controlled by processes within the hair follicles and the body's overall health, Popular Science reports.
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The results are surprising
Several scientific studies have examined whether the seasons influence hair growth.
Two small studies published in the British Journal of Dermatology found that the highest number of scalp hairs were in the resting phase toward the end of the summer.
At the same time, men's beards grew slightly faster during the summer months, but the difference was so small that it was barely noticeable.
A larger study involving 823 women, published in the journal Dermatology, found the same pattern.
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Overall, the research suggests that scalp hair does not grow faster during the summer.
On the contrary, the findings indicate that a greater proportion of hairs are in the resting phase at this time of year, according to Popular Science.
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