The US FDA has assigned the pregnancy category B status to Benadryl, which means that it is considered safe to use, as there are no known side effects. However, your doctor will be the best person to judge whether or not you should take Benadryl while you are pregnant. He will also decide on the quantity of intake.
Human carcinogen -- Benzene: Benzene is a chemical deemed to be carcinogenic to humans. The carcinogenicity of the substance may be influenced by the nature (e.g. inhalation, ingestion, skin contact), duration and level of exposure. Benzene exposure is associated mainly with an increased risk of developing leukemia or lymphoma.
Benzene is a colorless, flammable and toxic liquid with carcinogenic properties that has a sweet, gasoline-like odor. The chemical formula of benzene is C6H6, so it consists of six carbon atoms and six hydrogen atoms. Benzene is an aromatic hydrocarbon, which is a chemical compound consisting of carbon and hydrogen atoms with alternating double bonds forming a ring.