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)