It works by blocking a certain natural substance (histamine) that your body makes during an allergic reaction.

Monitor and control the formation of by-products during a reaction.

But that first step is difficult unless you can get down to the atomic level to see what is happening during a reaction.

People sometimes use arrow pushing to draw how electrons move around during a reaction.

Thus during a chemical reaction there is always an entropy change.

Instead, they are formed as reactive intermediates during a reaction.

A catalyst is not destroyed or changed during a reaction, so it can be used again.

During a reaction they may be reactants and/or products that react to form other products.

Allergens are what trigger a series of reactions by the immune system during an allergic reaction.

A common example is the removal of water generated during a reaction in boiling toluene.