This was my favourite of several allergy baooks that I've read recently. It's written by a mother (of a toddler with multiple allergies) in conjunction with a consultant pediatric allergist (also clinical lead for Allergy at a hospital in the UK, and a medical advisor to both Allergy UK and the Anaphylaxis Campaign, featured in The Times magazine etc...). This combination means an incredibly approachable book to read with solid medical expertise underlying it. There are also quotes interspersed through the book from other parents of babies & young children with allergies that share their experiences.
I found it really helpful in explaining the difference between an IgE-mediated (immediate) allergic response, non-IgE mediated (delayed) allergic response, and an intolerance. It's of particular relief for me because my daughter has a non-IgE mediated allergy and it can be difficult finding literature on this as its harder to diagnose.
The book explains different forms of allergy testing and identification, when these will work, and when they won't; i.e. blood and skin prick testing work for an IgE mediated response but not for a non-IgE allergy.
It also provides information on other atopic allergic reactions such as eczema, asthma, and allergic rhinitis and how these fit into the picture.