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.
This is because benzene is a carcinogen, which means it's a chemical or agent that can potentially cause cancer. The chemical formula of benzene is C6H6, so it has six carbon (C) atoms and six hydrogen (H) atoms. Its chemical structure can be described as a hexagon ring with alternating double bonds, as shown in this illustration. The chemical structure of benzene shows that for each carbon atom, there is one hydrogen atom. There are three ways to draw the chemical structure of benzene, which you can now see on screen. The illustration on the left (1), shows all the carbon and hydrogen atoms and how they are bonded together.