Illustration of two people, one who is covered in dirt and mud


Is being exposed to dirt good for you?

Could being too clean actually make you ill in the long run? Some people think that it is healthy for our immune system to encounter lots of foreign substances early on in life, so that it doesn’t become oversensitive.

This is the thinking behind the so-called hygiene hypothesis, proposed in 1989, which suggests that rising levels of allergies are linked to being too clean. There is evidence both for and against this hypothesis, and the picture is very complex and multifactorial. High standards of hygiene are important for protecting children from infection, and while it may be useful to expose them to certain pathogens, at certain doses, at certain times, we don’t know exactly what those are.

In recent years, the hygiene hypothesis has also come to encompass a whole range of diseases besides allergies, from diabetes to depression. But it is difficult to untangle the many factors that may contribute to a person’s risk of getting a disease. Genetics, diet, pollution and exercise may all play a role.

Lead image:

Illustration © Glen McBeth


About this resource

This resource was first published in ‘Immune System’ in January 2015.

Immunology, Health, infection and disease
Immune System
Education levels:
16–19, Continuing professional development