[DrDavid]

I heard it was due to exposure to cockroach feces. Really.

I think it is actually dust mite feces. These live in our beds and it is central heating that has helped them flourish.

[Ditter]

If I remember correctly from ,my last allergy testing, it is cockroaches themselves. After they have become dust particles they are the allergen. It was one of my allergies.

[Restorer]

I think it is actually dust mite feces. These live in our beds and it is central heating that has helped them flourish.

It is not central heating as such, although that may be one factor. It is a number of changes in buildings that maintains a higher average relative humidity. Dust mites die off rapidly when RH drops below 50%.