If you've been staring at your brush or your shower drain and feeling like you've been losing a lot of hair lately, don't freak out. A new British Journal of Dermatology study suggests that shedding more strands in the summer and fall is totally normal.
如果最近你老是盯着梳子或浴室排水阀，感觉自己掉了很多头发，千万不要惊慌。英国《皮肤病学杂志》刊出的一项新研究表明：夏天和秋天头发掉的比较厉害是完全正常的。

A seasonal pattern of hair loss has been long suspected; it's been observed anecdotally and documented in previous small studies. But those studies have focused on just one geographic location, so it hasn't been possible to know if those findings apply to everyone.
长久以来，人们一直怀疑掉发有季节规律。先前的小型研究已经观察到了这种现象。但这些研究只在某一区域进行，所以并不清楚是否对所有人适用。

Researchers at Johns Hopkins and Washington University changed that by compiling Google Trends data from eight countries in four hemispheres with high search rates for the term "hair loss." They looked at search volume from 2004 through 2016, and compared the data month to month and season to season.
约翰霍普金斯大学和华盛顿大学的研究人员通过编译来自四个半球八个国家的谷歌数据改变了这一情况，这些国家搜索"掉发"一词的频率很高。他们查看了从2004年到2016年的搜索量，并将这些数据按月份和季度进行比较。

Across all eight countries, the results were the same: People searched the Internet using phrases related to hair loss more frequently in the summer and fall compared to the winter and spring. The finding is relevant to doctors whose patients complain of hair loss in those two seasons, the authors say, and it may be useful in assessing how effective certain therapies are at treating the condition. But more research is needed, they add, to determine exactly why this pattern happens-and how much patients should care.
八个国家的结果都是一样的：与春冬两季相比，人们更频繁地在夏秋两季搜索与掉发相关的信息。研究作者表示，这一结果也与某些医生息息相关，这些医生的病人会在夏秋两季抱怨自己掉发；这一结果可能有助于评估治疗掉发的方法的有效性。他们补充道，还需要更多的研究来确定为什么会发生这一季节性规律--以及病人需不需要注意这个问题。

"Mildly increased hair loss in the summer and fall is normal," co-author Shawn Kwatra, MD, assistant professor of dermatology at Johns Hopkins University School of Medicine, tells Health. "This is speculative, but from an evolutionary perspective one of the roles of hair loss is to provide warmth," he says. "This would be less necessary during the summer months."
"夏秋两季有轻度掉发是很正常的，"合著作者Shawn Kwatra医学博士对《健康》杂志表示，他还是约翰霍普金斯医学院的皮肤病学助理教授。"这是推测性的，但从进化的角度来看，掉发的一个作用就是供暖，"他说道。"而夏季并不需要供暖。"

The tendency to grow thicker coats in the winter-and shed them in the summer-has also been documented in a variety of animals, including monkeys, cats, dogs, and camels. In humans, seasonal hair loss has been reported more in women than in men, Dr. Kwatra says, although the current study could not distinguish Google searches by gender. According to the American Academy of Dermatologists, it's normal to lose between 50 and 100 hairs a day.
冬季留长发，夏季剪短发的趋势在动物身上也很常见，包括猴子、猫咪、狗狗和骆驼。女性季节性掉发的情况比男性更多，Kwatra医生说道，虽然现在的研究并不能判别搜索谷歌的人的性别。据美国皮肤病学会资料表示，每天掉50至100根头发是很正常的。