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.
Definition. 1  As a noun, the common definition of chemical is a substance that is produced or used in a process (reaction) involving changes to atoms or molecules. The term is sometimes defined more broadly as a substance. 2  As an adjective, chemical means of or pertaining to chemistry. Chemistry is the study of matter and its transformations.