Why strong perfumes give you a headache

Perfumes on display at a shop on Moi Avenue in Nairobi. [Wilberforce Okwiri, Standard]

Humans can smell over 1 trillion odours. But no two people will react in quite the same way to the same smell. While there are some smells almost everyone agrees are unpleasant (such as paint thinner or rotten food), our reactions to other types of smells can be far more personal.

Take perfume. While one person may find the smell of a strong, floral perfume to be heavenly, another person may find it gives them a headache. There are many reasons why people can get a physical reaction to strong smells - but here are the three most common ones.