Humans are basically programmed to spring clean, says Anna O'Donovan at the Allergy Standards certification company. "Our pineal gland, a tiny endocrine gland buried deep in our brains, is responsible for the production of melatonin, and it is this melatonin that causes sleepiness in humans," she says. "The pineal gland responds to darkness, increasing its production in winter and reducing its output in summer so we do actually experience an ‘awakening' with the dawning of the longer days of spring." That provides a boost of energy that wakes us up earlier, gives us more motivation, and, during times when candles and lamps provided the only light, gave us a better idea of just how dirty our homes were. "Scientifically it really makes sense to clean our homes as the weather is getting warmer — the rising temperatures promote the growth of bacteria, so to prevent infection and disease, a good scouring is vital," she says.