Dr Adrian Morris is an allergy specialist and he explains why we think adults suddenly become allergic to pollen or foods or mites long after most people become allergic as children and the risk increases with increasing age. The outcome can be asthma, eczema or food allergies.
When we are a child and growing up our immune systems are rapidly developing and reacting to our environment so perhaps it is not too surprising when that is the time of our lives most of us acquire allergies & asthma, often after prolonged or repeated exposure to a particular allergen. Once our immune systems mature though this is clearly a much less common phenomenon affecting around 4 in 1000 adults who get asthma as adults.
We still do not have much idea why this happens though viral infection, depression and exposure to chemicals in the air or elsewhere in the environment (eg in the workplace) play a part in triggering the process. There is also an increasing amount of evidence that strongly suggests damp & mouldy homes can influence the development of respiratory diseases such as asthma in adults.
Some medicines are also thought to act a triggers; paracetamol and antacids prescribed for excess stomach acidity are known to increase risk of developing asthma. Perhaps not surprisingly there is also a risk when those same hormones that were involved in us growing up start to change during adulthood - so during pregnancy or menopause there is a chance of developing asthma or developing allergen sensitivity.