Science from Scratch

Laurence Pope, MSc Science Communication student explains the hygiene hypothesis.

Cleanliness isn’t always next to godliness; it’s actually possible to be too clean. The hygiene hypothesis states that a child growing up in an overly clean environment is left more susceptible to allergy development in later life. Allergic reactions occur when the body’s immune system overreacts and generates an inappropriate response to a harmless substance, such as pollen in hayfever. The effects of overreaction to pollen can range from a slightly runny nose to constriction of the airways and suffocation. By existing in an increasingly clean environment, a result of twenty-first century hygiene and healthcare improvements, a greater number of children aren’t sufficiently exposed to various infectious agents or parasites. Without exposure to such minor infectious agents, immune system development is skewed and the child fails to develop a well-balanced immune system. The hygiene hypothesis was put forward in 1989 in the British Medical Journal, as a way to explain why children in large families developed fewer allergies compared with only children – in large families infectious agents are more likely to spread from child to child. In short, send your kids outside – mud and dirt really are good for you!