There are lots of factors that contribute to how quickly our hair grows. Sometimes our hair grows slowly because of genetics, but there are also environmental factors that can cause our hair growth to slow down, such as seasonal changes. For example, our hair grows faster in summer and more slowly in the winter. But why? One reason for this is that during warmer weather, our blood circulates more freely, carrying nutrients more easily throughout our bodies, and enabling our bodies to produce more keratin (the protein that our hair is made of).
A second factor is that we usually get more vitamin D (the “sunshine“ vitamin) in the summertime. The sun makes our hair grow faster because our bodies synthesize UVB rays from the sun into vitamin D, which helps our bodies regulate keratin production. When we are deficient in vitamin D, this regulation misfires, triggering hair loss.
Our hair also grows faster in summer because we tend to leave our heads uncovered more than in the winter, which creates less friction and breakage. When we bundle up to stay warm in cold weather, we often add hats, scarves and hoods, which makes sense because we lose a lot of heat through our heads! But these coverings create more friction on our hair than we typically have in the summertime leading to increased hair fall due to cold weather.