How does one person (male or female) develop a form of food allergy towards peanuts, milk etc.?

Answer 1

http://www.webmd.com/allergies/foods-allergy-intolerance

Answer 2

This is a good web site from Ms Sue. There is also medical discussion on what triggers the allergy in the first place as some people suddenly can develop an allergy. It is thought that this may be due to an environmental trigger such as a virus which triggers the body's defence system to treat the protein in the allergen as an invader.

The susceptibility to the trigger seems to run in families so that often siblings have similar allergies, but these may start some time apart depending on when the environmental trigger occurs.

For example see coeliac http://www.enabling.org/ia/celiac/summary.html