If you have allergies, pregnancy can make your symptoms worse. But you're right to worry about taking allergy medicine during pregnancy. Pregnant women shouldn't take some allergy drugs. Certain antihistamines, however, are safe.
free radical. (chemistry). An atom or a diatomic or polyatomic molecule which possesses one unpaired electron. Also known as a radical.ree radical. in chemistry, a molecule or atom that contains an unpaired electron but is neither positively nor negatively charged. Free radicals are usually highly reactive and unstable.
Reaction, Chemical. the transformation of one or more substances into one or more new substances, differing from the original in chemical composition or structure. Both the total number of atoms of any given element and the chemical elements making up the substances remain unchanged during a chemical reaction.