It has long been recognized that there is an association between certain skin diseases and the differing seasons of the year, but in most cases precise relationships are not well known. Temperature, humidity, air movement, atmospheric pressure, sunlight, electrostatic charges, and cosmic radiation may all affect the skin from without or by such endogenous means as an influence on the general circulation or the basal metabolic rate. The influence may be exerted more indirectly through changes induced in micro-organisms, disease vectors, flora and fauna, work activities (fig harvesting, cotton picking), clothing habits, and the heating and ventilation of houses. Seasonally recurring cultural and religious customs (holiday hikes, sunbathing, feasts and fasts) also merit consideration. Although seasonal factors may sometimes be the primary causative agents of a disease they usually only serve to precipitate its onset or modify its development, intrinsic or "host" factors being of greater importance in most cases.
DOSTROVSKY A, EVEN-PAZ Z. Seasonal Factors in Pathogenesis of Skin Diseases. Arch Dermatol. 1961;84(5):750–758. doi:10.1001/archderm.1961.01580170044006