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.
Because of its chemical formula, C6H6, benzene is classified as a hydrocarbon, which is a compound that consists of only carbon and hydrogen atoms. Its structure and formula reveal benzene to be an aromatic hydrocarbon, which is defined as a compound that is composed of hydrogen and carbon that has alternating double bonds forming a ring.