Spring fever’s symptoms usually appear during the onset of the vernal equinox. In the northern hemisphere, people begin to feel more energetic, enthusiastic, and amorous because of chemical changes in the body, in part, produced by increased exposure to daylight. Scientists cite a number of factors that contribute to spring fever. It starts with increased light that sends a signal to the brain’s pineal gland, which then reduces its production of melatonin, a hormone that regulates our body clock and controls our mood and energy levels.

As the days grow longer, the chemical disappears and leaves people feeling more energized and confident. Increased light also affects the hypothalamus, the section of the brain that regulates eating and sleeping.

Our other senses—sight, smell, and hearing—also wake up as blossoms and spring breezes assault them. Such stimuli can trigger strong emotions, from euphoria to sadness.