What is it? Citric acid
Other names it goes by: 2-Hydroxy-1,2,3-Propanetrirboxylic acid; Monohydrate citric acid.
What's it used in? Shampoo, liquid soaps and cleansers, conditioners and moisturisers.
What does it do? A weak organic acid, it's a natural preservative and acts as a chelating agent, which means it allows cleansers to produce foam.
Any controversy? It's on the list of Canadian prohibited and restricted cosmetic ingredients. There are concerns it can affect the brain and nervous system even at low doses.