Does Cortisol Change With the Seasons? What Small Studies Suggest

As the days shorten, social media fills with advice about "winter cortisol" and products said to bring it back down. It is a fair question whether the stress hormone really follows the calendar, because daylight, temperature, and routines all change with the seasons. The honest answer is that there are hints of a pattern, but the research is limited and the practical meaning for your skin or your stress levels is unclear.

First, the basics that are well established. Cortisol is a hormone released by the adrenal glands through the HPA axis, the body's main stress-response system. It follows a daily rhythm, typically highest shortly after waking and lower in the evening. That daily pattern is far larger and more reliable than anything researchers have reported across seasons, so a single reading depends heavily on the time of day it was taken.

Now to the seasonal evidence. A study published in Behavioral Medicine in 2000 followed 147 adults (72 women and 75 men) for a year and measured salivary cortisol. The authors reported that levels were significantly higher in winter and fall than in spring and summer, and they concluded that researchers running long studies should account for the time of year. That is a useful finding, but it is one study from the year 2000 and it tells us about group averages, not about how any single person will feel.

A different method points the same general way, with caveats. A 2015 study in Biomarkers measured cortisol in hair samples from 27 Hispanic women living in an agricultural region of Washington State. Hair reflects cortisol over roughly the preceding couple of months, and the researchers found higher levels in fall samples than in summer samples. The authors themselves noted the small sample, the single region, and that the study could not test why the difference appeared. Possible explanations such as daylight, weather, or work and school schedules remain speculation.

So what is proven and what is trend? Reasonably supported: cortisol varies a great deal across the day, and some studies suggest modest differences between seasons, with higher values reported in colder months. Not established: that these differences are large enough to cause symptoms, that they affect skin in a measurable way, or that any supplement, tea, or "cortisol-balancing" product can correct a seasonal shift. Marketing that treats winter as a cortisol problem to be fixed goes well beyond what the studies actually show.

If your skin or mood changes in colder months, there are many well-understood reasons that have nothing to do with cortisol, including drier indoor air, less sunlight, and disrupted sleep. Steady sleep and wake times, daylight exposure when possible, and a gentle moisturizer routine are sensible regardless of the hormone story. If you are worried about persistent exhaustion or other symptoms, a clinician can order appropriate tests rather than guessing from the season.