**5. Toxic effects of phenolic compounds on humans**

Most phenolic compounds can easily penetrate the skin through absorption and can read‐ ily be absorbed from the gastrointestinal tract of humans. Once in the system, they undergo metabolism and transform to various reactive intermediate forms particularly quinone moi‐ eties, which can easily form covalent bonds with proteins, resulting in their ability to exert toxic effects on humans [35].

Chlorophenols, aminophenols, chlorocatechols, nitrophenols, methylphenols and other phe‐ nolic compounds have all been characterised as exerting toxic influence on humans [36]. Bisphenol A and some alkylphenols have been identified to exert endocrine disrupting effects on humans by altering the development of mammary glands in exposed animals [37]. Similar work also discloses the tendency of bisphenol A to delay the onset of puberty in girls [38]. Consumption of liquids, including drinking water, containing a high concentration of phenol results in problems with the gastrointestinal tract and muscle tremor with difficulty in walk‐ ing. Application of products containing a high concentration of phenol to the skin causes blisters and burns on the skin; heart, kidneys, and liver damage may occur with exposure to high levels of phenol [39]. Because of their tendency to readily oxidise to quinone radicals, which tend to be more reactive, catechols have the tendency to cause DNA damage or ary‐ lation, destroy some proteins in the body and disrupt transportation of electrons in energy transducing membranes [35]. Caffeic and dihydrocaffeic acids, in the presence of copper, also cause damage to DNA [40]. Chlorophenol poisoning causes mouth burning, throat burning and necrotic lesions in the mouth, stomach and oesophagus. It also induces abnormal tem‐ perature and pulse fluctuation, weak muscles and convulsions [41]. Other effects of chloro‐ phenol poisoning include damage to the liver, kidneys, lungs, skin and the digestive tract [42]. Hydroquinone also damages chromosomes. Para‐cresol and 2,4‐dimethyl phenol have been classified as a chemical with the potential of inducing carcinogenic effects [43].
