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.
n, pl -tries. 1. (Chemistry) the branch of physical science concerned with the composition, properties, and reactions of substances. See also inorganic chemistry, organic chemistry, physical chemistry. 2. (Chemistry) the composition, properties, and reactions of a particular substance. 3. the nature and effects of any complex phenomenon: the chemistry of humour. 4. informal a reaction, taken to be instinctual, between two persons.