The Science Behind Spring Fever

Lucy Bell-Young

by Lucy Bell-Young

25th April 2018

Every mammal experiences it, poets have been writing about it for centuries, but scientists are only just starting to get a handle on it. We’re talking about Spring Fever, of course, but does this seasonal phenomenon have any scientific basis?

What is Spring Fever?

Although it is not recognised as a “definitive diagnostic category,” spring fever affects most mammals in the northern hemisphere. It can be characterised by a few things, including:

  • An increase in energy
  • A sense of comfort
  • Daydreaming
  • Amiability
  • Lack of ambition
  • An increase in sexual desire

Spring fever replaces the winter blues we all feel, the symptoms of which can be associated with cabin fever. If you notice a drastic change in your mood when the weather gets warmer, or tend to feel happier and more content, then you’re probably experiencing some form of spring fever.

Flowers blooming in a tree, marking the start of spring and Spring Fever

What Causes Spring Fever?

The onset of spring fever is in line with the spring equinox. Latin for “equality of night and day,” the spring equinox marks the moment the sun moves north across the celestial equator. This happens because of the Earth’s axial tilt which, at the time of the equinox, is perpendicular to the sun’s rays.

For those in the northern hemisphere, the spring equinox marks the beginning of warmer months. However, for those in the southern hemisphere, it marks the beginning of autumn – sorry, Australia.

This year, the spring equinox fell on March 20th. This means that even though Britain has been shivering under a blanket of grey clouds and rain, spring officially began in March. This saw the beginning of longer days, brighter days, and – eventually – warmer days.

This is what causes spring fever. By being torn out of their wintry slump, people undergo very specific responses to these brighter mornings and nights. In the past, it was thought that these responses were purely psychological; but now, research points towards a more physiological reaction that all creatures of nature experience in spring.

Mood and Energy

The hormones in our brains and bodies are dramatically affected by sunlight and darkness. When it’s dark, a hormone called melatonin is released. Also known as the sleep hormone, melatonin is produced by the pineal gland and controls our sleep. It does this by sending a signal to the brain when it’s dark, saying that it is time to get some shut-eye.

This is why in winter months, when there is little sunlight and the days are shorter, we tend to feel more tired, sluggish and demotivated. It is also why some people suffer from Seasonal Affective Disorder (SAD).

Spring, on the other hand, increases levels of serotonin in the brain while decreasing levels of melatonin. This happens because of the extra sunlight and longer days. Serotonin is an important neurotransmitter and a big contributor to feelings of happiness and well-being. In fact, low serotonin levels have often been linked to depression.

The longer and brighter days that spring is characterised by actually increase serotonin levels in the body. Meanwhile, the extra bit of sunlight means that melatonin production is reduced. This could be a reason why spring fever causes people to feel happier and more energetic.

Sun ray hitting the tips of grass

The Birds and the Bees

Promoted feelings of happiness, comfort and energy go hand-in-hand with another emotion enhanced by spring fever: love. In spring, people generally become more susceptible to romance and falling in love.

In fact, it has been recorded that birth rates are higher in March than any other time of year. It has also been observed that towards the end of spring, there is an increase in the production of the luteinizing hormone. This fuels our primal desire to engage in reproductive behaviour as it increases testosterone in men and encourages ovulation in women.

This observation has been made throughout history. As Lord Tennyson wrote in his 1835 poem, “In the Spring, a young man’s fancy lightly turns to thoughts of love.” But there is more to this than butterflies and crushes – it all comes down to basic survival instinct.

Survival Instinct

Humans aren’t the only mammals affected by spring fever. Like us, many other animals follow a seasonal pattern when it comes to mating; and this pattern of reproduction is all about the continuation of the species by ensuring that the offspring have the best chances of survival.

Mice, for example, have more frequent spikes in birth rates in areas that are further from the equator. This is because seasons aren’t as distinctive in regions that are close to the equator given the dominance of sunlight and heat.

So how do mammalian bodies identify seasonal changes in order to encourage breeding? It all comes down to an internal biological body clock. Yes, they do actually exist and go by the name suprachiasmatic nucleus (SCN).

Located in the hypothalamus at the base of the brain, the SCN helps to keep mammals running within a 24 hour timeframe. This synchronises behavioural patterns (like sleeping, eating, waking and breeding) with cycles of the day.

The way the SCN is able to do this is by monitoring light. When our eyes detect light, it is passed through a pathway to the retina. This then transfers information to the pineal gland about the length of a day. As we now know, the pineal gland controls the production of melatonin. Therefore, in spring, the increased amount of light results in a decreased amount of melatonin. The internal body clock then tells the animal that this is the optimal time for reproducing.

Macro shot of daisies

Spring is the season of renewal, rebirth and new beginnings. It fits well, then, that this spring marks ReAgent’s official move into its new manufacturing facility! With over 38,000 square feet at our disposal, new production facilities, and built-to-spec as well as eco-friendly features, we’re experiencing a different kind of spring fever! If you missed our recent announcement, you can click here to stay updated. 


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