Many skin functions are circadian
rhythmic. The proliferation of skin cells varies by up to 30-fold in the
24 hours, being greatest at midnight and least at noon (1). In women,
blood flow, amino acid content and water loss are roughly 25 percent
higher at night than morning or afternoon. These rhythms persist in oral
contraceptive pill users, although the rate of water loss and blow flow
is greater by 10 percent while the content of amino acid is reduced by
35 percent (2). Oil production by skin glands is twice as great at noon
than between 02:00 and 04:00. The skin is more acidic during sleep than
around midday and its temperature is higher in the evening than morning
(3,4). Skin temperature must be about a degree higher at 16:00 compared
to 04:00 before sweating begins, although sweat production is greater in
the afternoon than morning (5,6).
Day-Night Differences in Skin
Circadian rhythms in skin biology give
rise to day-night differences in the texture, radiance and overall
appearance of facial skin. A group of French women self-rated the
natural appearance of their facial skin best around 10:00 and worse at
night. The same women found the effect of a restorative rejuvenating
cosmetic preparation (Noctosome, Lancome) depended on the time of its
application. Bedtime application had a significantly better effect,
particularly in women between 25 and 35 years of age and ones of fair
complexion. The better effect of the nighttime application was
anticipated since the product was specifically designed to work in
relation to the known circadian rhythms of facial skin (7).
Circadian Rhythms in Skin Disorders
Psoriasis: Psoriasis is a chronic
inflammatory disease that typically produces a bumpy, flaky condition of
the skin especially areas of the scalp, elbows, knees, and back. The
cell proliferation rate of the affected skin is much higher than normal
skin and shows marked circadian variation (8). In the epidermis, the
cell proliferation rate in areas of psoriasis is highest between 21:00
and 03:00 and least at 09:00. However, in the dermis the rhythm is
reversed; cell proliferation is greatest at 09:00 and least at 03:00
(9). The inflammatory activity of psoriasis also varies greatly. It is
highest at night and lowest in the morning (10).
Atopic Dermatitis: Atopic dermatitis
is a chronic inflammatory disease which shows marked circadian variation
in the intensity of symptoms. Itching is most intense late in the
evening and may disrupt nighttime sleep (11). The day-night pattern in
the severity of the itching seems to be dependent on the circadian
rhythm of the skin’s sensitivity to histamine, which is highest at
Skin Cancer: The experimental study of
circadian rhythms in the susceptibility of skin to tumor induction in
humans is not possible. However, it can be easily done in laboratory
animals by applying tumor-causing chemicals at various times of the day
and night. Results show the risk of developing skin cancer differs
dramatically with the time of the day of their application. Generally,
tumor development is greater when contact occurs in the animal’s
activity span (when the genetic or DNA material of skin cells is
replicating) than in the rest period (13,14,15). These findings may
imply that human beings are at greater risk when regularly coming in
contact with cancer-causing agents in the late afternoon and evening.
Skin Rhythms Affect Diagnostic
Allergy Testing: Most allergy tests
involve the injection of a small quantity of allergens like house dust
extract or different kinds of pollens just under the skin of the upper
arm or back. Positive responses are shown by the development of large
red areas with light-colored swelling in the center. The time of day and
time of menstrual cycle allergy tests are done influence their results.
The skin is much less reactive to testing early in the day than
afternoon and evening. This means the severity of allergies and even
exact identification of specific sensitivities may be misjudged when
tests are conducted early in the day (16). Menstrual cycle variation in
skin reactivity also occurs in young women not using oral
contraceptives; it is greater by about 25 percent at menstruation than
Tuberculosis Testing: The tuberculin
skin reaction of persons who had past exposure to the bacteria is nearly
3-fold greater when testing is done at 07:00 rather than at 22:00 (18).
Circadian Rhythms of Skin
The effects of cream and patch
medications show circadian periodicity. Twice as much of lidocaine is
taken up by the skin when applied as a cream at 16:00 than at 08:00
(19). The rate at which nicotine penetrates the skin is several-fold
faster at 04:00 than in the afternoon (20). The pain-deadening effect of
lidocaine lasts 2-3 times longer when injected into the skin at 15:00
than at 07:00 or 23:00; the pain-deadening effect of betoxycaine lasts 2
times longer when injected at 15:00 than in the morning or evening (21).
The activity of a popular topical anti-inflammatory corticosteroid cream
medication is greater when applied in the afternoon than morning (22).
1. Certain cosmetic products are
fabricated for application at specific times of the day. Use them as
directed to ensure they work with skin rhythms.
2. Apply skin creams and ointments
that retard moisture loss at night to reduce the depth of wrinkles and
give the skin a more youthful look.
3. The results of allergy and medical
tests that are applied to the skin maybe strongly affected by the time
of day or day of the menstrual cycle they are done.
4. There are time or day differences
in the efficiency of pain and other patch medications and adjust the
dosing time of their application to improve effects.
*Summary of background information for chapter 15 in:
SMOLENSKY M.H. and LAMBERG.L : Body Clock Guide to Better Health ;
H.Holt , NY., 2001
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in the production of tumors. Journal of Pathology and Bacteriology.
(14) Frei JV, Ritchie AC. Diurnal
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(17) McGovern JP, Smolensky MH,
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(18) Cove-Smith JR, Pownall R, Kabler
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penetration of methyl and hexyl nicotinate. Life Sciences.
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