verb
-acts; -acted; -acting
[no obj]
to behave or change in a particular way when something happens, is said, etc.
of a chemical substance :to change after coming into contact with another substance - often + with
medical :to be affected by a drug, food, etc., in usually a bad way
react against
[phrasal verb]
react against (someone or something) :to do things that are opposed to (something or someone that you disagree with)