Spring fever, that reputed and seemingly infectious malady that strikes when the days lengthen and temperatures begin to climb, has been blamed for feverish bouts of house-cleaning, restless behavior in the classroom, distraction in meetings and love struck dazes.
Some scientists think spring fever is more than just a colloquialism -- they think it's a constellation of symptoms brought about by hormonal changes in the body.
In winter, the body secretes high levels of melatonin, a hormone that governs sleep-wake cycles. Come spring, the increasing amount of daylight is registered by light-sensitive tissue in the eye, which signals the brain to stop secreting so much melatonin. As the hormone's levels drop off, greater wakefulness results.
On the other hand, levels of another chemical, serotonin, rise in spring. This mood-elevating neurotransmitter may be at the root of the giddiness, energy boost and enthusiasm that characterize spring fever.
Anthropologists have suggested that spring fever may have developed over the course of human evolution. They point out that early humans often spent winter in a state of near-hibernation. Then, when spring arrived, they would enter an active period of intense hunting, gathering and procreating.
Attractive though that theory may be, it doesn't quite explain the state of the early American colonists come spring. Historians think the colonists coined the term spring fever to refer to the weakness, fatigue and irritability many felt after a long winter without fresh fruits or vegetables. (Technically, the colonists' symptoms were that of scurvy.) Such etymology suggests that the term spring fever is a remnant of times past that's been co-opted to mean something different today.
But there's no doubt that the body's internal chemistry and susceptibility to illness changes with the seasons. Just as scurvy outbreaks once peaked in spring, so did measles and rubella before wide-scale vaccinations became available. Attacks of the painful joint inflammation known as gout peak in April.
Dermatologists notice more cases of dermatitis and rosacea, and allergists, not surprisingly, field surges of complaints about hay fever in spring. Also, obstetricians have reported spring to be a season of exceptionally high rates of unplanned pregnancies. (Scientists are uncertain as to what's behind this last effect, though unusually high springtime sperm counts in men offer some clue.)
Spring also is marked by higher rates of suicide, a trend psychologists have struggled to explain.
On the plus side, spring is also the season in which people bid a temporary farewell to flu, seasonal affective disorder and heart attacks, all of which peak in winter. People also experience a springtime drop-off in catching sexually transmitted diseases, which goes hand in hand with the rather paradoxical fact that people tend to have less sex in spring.
In fact, many of spring's effects on the human mind and body are seemingly contradictory. Hormones do a partial job of explaining the seasonal epidemic of impulsive, giddy and amorous behaviors observed as the memory of winter fades, but much about the season's influences remains mysterious.