Preservatives

A preservative is a chemical that is added to a food product to artifically lengthen its shelf life and prevent spoilage.
There are two main types:
Antioxidants - which absorb oxygen and stop bacteria growing , however since they take oxygen away from the food they can modify the texture and/or taste of the product, meaning more additives must be added to correct this. Typical antioxidants are Butylated hydroxyanisole (BHA)(E320) and Butylated hydroxytoluene (BHT)(E321).
Anti-microbial preservatives such as sodium nitrate(E251) and EDTA(E385). These prohibit microbial growth so there is great concern in humans ingesting them as they may be harmful.

Many studies point to synthetic preservatives and artificial coloring agents agravating ADD & ADHD symptoms in those affected.