# Does Summer Really Accelerate Hair Growth? Scientific data examines the impact of sunlight and temperature on the hair growth cycle. - **Source:** [Popular Science](https://brifing.si/source/cc3d313a-759c-4802-b881-fc8585f35ef9) - **Published:** 2026-07-19 - **Original article:** - **On Brifing:** https://brifing.si/s/dd07283e-5a20-4620-b346-3432cb5d3459 ## Hair Growth Phases Hair follicles go through four phases: anagen (growth), catagen (transition), telogen (resting), and exogen (shedding). This cycle is influenced by genetics, nutrition, and stress. On average, hair grows about 5 inches per year, but this duration shortens with age. ## Seasonal Growth Claims A common belief suggests increased sunlight and vitamin D synthesis in summer boosts hair growth. However, dermatologist Houshmand states there's no proven significant effect of extra vitamin D on growth for those without deficiency. ## 1990s Research Findings Two small-scale studies in the British Journal of Dermatology showed scalp hair was most in growth phase during March. While beard growth increased 60% in summer, this translated to only 0.3 inches extra monthly growth. ## Landmark 823-Woman Study A 2009 study with 823 participants revealed hair follicles were most frequently in resting phase during summer. Similar patterns were observed in alopecia patients, indicating seasonal variations lack clinical significance. ## Sun's Other Effects While controlled sun exposure boosts serotonin production, dermatologists emphasize climate change won't reverse receding hairlines. Excessive UV radiation can actually damage hair strands. ## Scientific Consensus Current evidence doesn't support claims of significant summer hair growth acceleration. Balanced nutrition, stress management, and dermatological care prove far more critical for hair health than seasonal factors. ## Sources covering this story - https://www.popsci.com/science/summer-hair-grow-faster/ — --- _Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._