Do Hair And Nails Really Grow Faster In Summer?

Our hair and nails are constantly growing, but not at a constant rate – indeed, everything from our hormones, to our nutrition, to age, to simple genetics can affect how fast they grow. But what about something not connected to our bodies at all? What about the season?

You may have heard that our hair and nails grow faster in the summer. It doesn’t make a whole lot of sense, since that’s when you need the extra coverage the least, but is it true? The answer, perhaps surprisingly, is… yeah, kinda.

Does hair grow faster in hot weather?

We repeat: kinda. Basically, the evidence is there, but it isn’t overwhelming. 

There are some small studies that have shown, for example, that beard growth is fastest in hot months, and that the amount of resting hair on the head – i.e., not actively growing or shedding – is highest at the end of summer. Overall, though, that’s just not enough to prove the statement definitively.

Perhaps easier to answer is why such a seasonal speed-up might occur. “It's possible that the warmth causes an overall increase in blood flow, which increases circulation,” Robyn Gmyrek, a board-certified dermatologist at Park View Laser Dermatology, told Bustle in 2020.  “[That], in turn, increases the amount of nutrients and growth factors delivered to the hair follicle.”

There’s a caveat, though. What evidence we do have of increased hair growth puts the maximum rate at about 60 percent faster than the minimum – and that sounds like a lot, but you have to remember that the baseline hair growth speed is less than half a millimeter a day. In other words, even if your hair does grow faster in the summer, it’s not going to really be so much that you notice.

If you do notice, then it’s probably because of a summery side effect. “I think that because people are wearing less clothing and many women are shaving the exposed body parts, they are acutely aware of any growth,” Gmyrek said. “Even a millimeter or two.”

Do nails grow faster in hot weather?

With nails, the picture is clearer: yes, nails grow faster in summer than in winter – or, at least, they should.

That may partly be for the same reason as your hair – more blood flow – but there are a few hints that the picture is more complex than that. “There are differences [in growth rate] from finger to finger,” Lawrence Norton, then a clinical professor of dermatology at the Boston University School of Medicine, told the New York Times back in 1988. “The middle and fourth finger tend to grow a little faster than the fifth and the thumb.”

Similarly, the nails on your right hand probably grow faster than those on your left – unless you’re a southpaw, in which case you can reverse that – and injured fingers, or fingers going through a period of sickness, can slow down nail growth dramatically. 

That we know all this is thanks to just one or two guys and their weird, decades-long obsessions with monitoring nail growth. Starting in 1941, a physician named William Bean undertook what may well be the longest ever longitudinal self-study of the topic: every month, he would scratch a line right at the start of his fingernail, and every month, at the same time, he would measure precisely how far previous scratches had moved. 

Across more than four decades of observation, he found countless little points of nail-related interest: injuries and blemishes will usually just grow out with the nail, he found; mumps will slow down the growth almost to the point of stopping it completely, while influenza is not so dramatic. He also logged a steep deceleration in nail growth after age 40 – not a gradual decline, but a sharp drop-off, which he recorded with a rather poetic flourish: “The subtle graying of the hair, the slower pace of running, walking, or climbing stairs, the encroachment of presbyopia, to which I surrendered by getting bifocals at the age of 55, compare with the stark and finite memento in the diminuendo of nail growth,” he wrote in 1974.

“If one forgot the shifting baseline and concentrated on absolute rate of growth, he might conclude that the last three years had been worse than having mumps,” he joked.

But here’s the weird thing: contrary to most of the studies before him, Bean actually found no seasonal difference at all in his nails’ rate of growth. During the decades of his study, he never noticed changes related to heat, or geography, or physical activity – even though he freely admitted that such changes had “good evidence” supporting them.

So why do we say your nails should grow faster in warmer weather, if Bean never found such an effect? And why did he believe it himself? Well, just like how we transformed our mouth shape with smushy food, Bean thought, we may have sort of… evolved ourselves out of this natural pattern.

“I have never observed the [seasonal] trend, even though the method was accurate enough to have discovered it,” he wrote in his 1963 paper A Discourse on Nail Growth and Unusual Fingernails. “My suspicion is that spending so much time indoors with central heating and air conditioning […] I do not have enough exposure to climatic extremes.”

The verdict

So, next time someone asks whether hair and nails grow faster in the summer, or if that’s just their imagination, you’ll know what to say. Yes, their growth does accelerate – but at the same time, assuming they spend a reasonable amount of time indoors, they’re also probably imagining it to some extent.