Seasonal Hair Shedding: A Late Summer/Fall Shed Really Does Occur
Moulting of hair is common in various animals. Moulting appears to be controlled by a variety of endogenous and exogenous factors. Both changes in air temperature and sunlight exposure likely play a role in how animals shed hair. Overall, sunlight exposure appears to be far more important than actual changes in temperature.
Variation in daylight hours is thought to be very relevant for how mammals shed hair. Many mammals, but not all, grow a winter coat and then shed it to have a lighter coat during summer. Horses for example tend have a winter coat but some donkeys do not show such variations in coat characteristics. Understanding seasonal changes in animal coats has been important in the wool industry as promotion of better wool production has clear benefits. In cashmere goats, reducing the length of sunlight can increase anagen phase and increase cashmere production. The same is true of wool production in sheep.
In humans, seasonality of shedding was not thought to exist in some of the early medical literature. In 1969, Orentreich offered support for a seasonality of hair shedding when he reported three women in New York who experienced maximum hair fall in the month of November. Orentreich also proposed that a second lesser peak occurred in Spring. To date there have been five important studies which support seasonal shedding phenomenon in both men and women.
Seasonal Shedding: 5 Key Studies to know about
Study 1: Randall and Ebling, 1991
Randall and Ebling studied the hair growth parameters every 28 days of 14 healthy males.
The study was a fascinating one whereby 14 men age 18-39 in Sheffield UK collected beard shavings, shed hair, as well as finger and toe nail clippings every 28 days for 18 months. In addition, every 28 days, hair samples were taken from the study participants from 5 areas of the scalp. The participants were also asked to record the number of hours they had spent outside.
Men in the Randall study reported spending more time outdoors in summer than in winter – about 30 hours per week in June and July compared to 11 hours in January and February.
The authors found that the proportion of hairs in anagen (by pluck tests) reached peak in March each year and then fell steadily through September. This findings was true for all areas of the scalp studied including the vertex parietal and occipital areas of the scalp. When the authors examined the bags of hair that were collected from participants, they found that shed hair was maximal in August and September and least in March. In fact, the number of hairs lost per day in August was 60 and this was about double the number of hairs loss in March. Interestingly the diameter of growing hairs did not change.
Beard growth had a different pattern to that of scalp hair. Beard growth was maximum in July and was lowest in January and February. Finger and toe nails did not show seasonal variations in growth.
Study 2: Courtois et al, 1996
The Courtois study from L’Oreal Laboratories in France was a fascinating one which involved studying 10 subjects over a period of 8 to 14 years. Four of these patients did not have other forms of hair loss and 6 did. The authors used phototrichograms to document the percentage of hairs in telogen phase as well as standardized hair collection techniques to determine hair shedding rates.
What was remarkable in the detailed study was that the percentage of hairs in telogen varied quite significantly in all patients – but particularly among those with other forms of hair loss.
In 9 of the 10 subjects, there was a link between sunshine hours and percentage of hairs in telogen. The authors found that late summer and early Autumn (August, September and October) were periods of the highest telogen percentages and December January and February were the periods of minimal shedding. The authors identified a smaller peak of shedding in Feb and March. The authors found that the peak hair shedding from hair collections followed the peak telogen rates by 1-2 months.
Study 3: Pieard-Franchimont and Pierard, 1999
The authors performed trichograms of 2857 subjects over 2 consecutive years. They found an increased proportion of telogen effluvium between July and October. The lowest rates were found in January.
Study 4: Kunz et al 2008
A 2008 study from Switzlerand by Kunz, Seifert and Trueb examined shedding patterns in 823 women using trichograms. The authors found that telogen rates were lowest at the beginning of February and highest in July. There was a second peak noted by the authors in April it was less pronounced than in summer. What was remarkable about the Kunz study was just how many women were studied. Certainly, a study of 823 women is quite large. Second, the authors showed that this seasonal shedding occurred regardless of whether or not the patient had female pattern hair loss and regardless of whether or not they were using minoxidil.
Study 5: Liu et al, 2014
Liu and colleagues studied seasonal changes in hair growth patterns in 41 male and female volunteers from China. Phototrichograms were used to record the percentage of hairs in anagen and telogen. The authors showed that the highest proportion of telogen hairs were in September and lowest in January. In women, these proportions rose form approximately 8 % in January to 12 % in September.
CONCLUSIONS: Why is seasonal shedding important to know about?
The five elegant studies to date support that notion that hair shedding increases in late Summer and Fall for humans.
We don’t really know why humans shed like this although it is proposed that climate factors are very import for humans. We know that mammals moult and patterns of moulting are quite different for different mammals. It has been proposed that delaying shedding until the end of the summer might help protect humans from ultraviolet exposure during summer.
These changes in growth may be related to many factors including hormones. It’s interesting that beard growth peaks in the summer in men as it has also been shown that plasma testosterone levels also rise somewhat during the summer and then fall to their lowest levels in January and February. But a variety of factors likely contribute to these shedding patterns including melatonin, testosterone, thyroid hormones, prolactin.
These studies are important for patients that come into the office. We need to always take into account the phenomenon of seasonal shedding when evaluating patients. Suppose a patient starts a treatment and is doing really well. In April and May she tells you that she’s so pleased with her hair. Her hairdresser is amazed with her hair. Her friends have noticed a change. Now in September she contacts you and she is extremely upset. Her hair is shedding terribly. She has lost ground. Of course, you need to consider all the factors. Is she using the right medications? Is their actually another diagnosis present? But seasonal shedding needs to be considered.
A 2017 study in the British Journal of Dermatology also supports that people are more concerned about hair loss in the Summer and Fall than in the Winter and Spring. Specifically, a study by Hsiang and colleagues looked at the Google Trends for the search term “hair loss” in Summer, Fall, Winter and Spring. Compared to the Spring, searches were 5.74 times more frequent in Summer and 5.05 times more frequent in Fall compared to the Spring. Searches about hair loss in Winter were 2.63 times more frequent in Winter than Spring. Spring was a time of least entries related to hair loss.
Reinberg A et al. Circadian and circannual rhythms in plasma hormones and other variables in five healthy young males. Acta Endocrinology 1978; 88: 417-27
Smals AGH et al. Circannual cycle in plasma testosterone levesl in man. J Clin Endocrin Metab 1976; 42: 979-82.
Orentreich N. Scalp hair replacement in man. In: Advances in Biology of Skin. Vol IX: Hair Growth. (Montagna W, Dobson RI, eds). Oxford: Pergamon. 1969. 99-108.
Courtois et al.Periodicity in the growth and shedding of hair. Br J Dermatol, 1996 Jan;134(1):47-54.
Hsiang EY et al. Seasonality of hair loss: a time series analysis of Google Trends data 2004-2016. Br J Dermatol2018; 178(4):978-79
Maurel D et al. Effects of photoperiod, melatonin implants and castration on molting and on plasma thyroxine, testosterone and prolactin levels in the European badger (Meles meles). Comp Biochem Phyiol A Comp Physiol. 1989;93(4):791-7.
Zhang et al. Comparative study on seasonal hair follicle cycling by analysis of the transcriptomes from cashmere and milk goats. Genomics 2019 Feb 16
Liu et al. A Microarray-Based Analysis Reveals that a Short Photoperiod Promotes Hair Growth in the Arbas Cashmere Goat, PLoS One. 2016 Jan 27;11(1):e0147124.
Pearson AJ et al. Inhibitory effect of increased photoperiod on wool follicle growth. J Endocrinol 1996 Jan;148(1):157-66.
Dr. Jeff Donovan is a Canadian and US board certified dermatologist specializing exclusively in hair loss. To schedule a consultation, please call the Whistler office at 604.283.1887