Did you know that skin seems to be more permeable in the evening and at night, right when the evening routine takes place?
A rhythm we cannot see
Many body functions follow a cycle of about 24 hours, the circadian rhythm. Sleep, body temperature and hormones change regularly between day and night. Until the 1990s, though, there was little data on how this rhythm applies to the skin.
The question matters for anyone who cares for their skin. If the skin barrier behaves differently at different times of day, the moment we apply a product could matter too.
How the study was done
The study, published in 1998, involved 16 healthy volunteers, nine men and seven women aged 23 to 53. Over a full day the researchers measured four skin values every two hours. Water loss through the skin, hydration of the outermost layer, pH and temperature.
The measurements were repeated on four areas of the body, the forehead, forearm, upper back and shin, for a total of twelve readings for each value. The data were analyzed with statistical methods designed to detect rhythms.
What was observed
Most values showed a pattern linked to the time of day. Water loss, pH and skin temperature followed a statistically significant circadian rhythm on the forearm, forehead and shin. The exception was the hydration of the outermost layer, which showed no rhythm.
Differences between peak and low were present in every area. The same value measured in different places changed in a similar way, while different values were not linked to each other. According to the authors, these results suggest that the skin is more permeable in the evening and at night than in the morning.
How to read the result
This is a small study, with 16 people and measurements over a single 24-hour period. The authors themselves speak of results that suggest, and point to a possible relevance for applying products to the skin, without turning it into precise rules.
Read with caution, the finding gives the evening routine one more reason to exist. Evening is when the skin seems more permeable, and it is also when we have more time to care for it calmly. To decide what to use at night and what in the morning, especially with active ingredients, a dermatologist remains your best reference.
This article is for information only. It does not replace the advice of a doctor or dermatologist, whom you should consult with any question about your skin.