Some typical symptoms indicating your child may have a phenol problem are [not all of these need be present]: dark circles under the eyes, red face/ears, diarrhea, hyperactivity, aggression, headache, head banging or other self-injury, inappropriate laughter, difficulty falling asleep at night, and night waking for several hours. The typical adult symptom of phenol intolerance is chronic fatigue syndrome, which is the opposite symptom that most children have, altho some children do present as always tired/lethargic, instead of hyper with sleep and other issues.
Phenols are chemicals found in basically all foods. The "phenol" category contains quite a few subgroups, both food and non-food. For example, salicylate is a subgroup of phenol. There are other chemicals found in foods that can cause similar symptoms as phenols, including amines, even tho they are not technically "phenol".
For some children, their bodies have difficulty processing the phenols into useful or at least non-harmful substances. This condition is called PST deficiency. So you need to reduce your child’s phenol intake, or help his body process them. Otherwise they build up to levels which can affect his behavior and physical condition.
Phenols -- "A group of natural and synthetic compounds that are ingested or produced to varying degrees by the body or by microbes in the intestine contain a benzene ring with one or more hydroxyl (OH) groups attached to it. When this attachment occurs, they become phenolic compounds. These compounds possess unique chemical properties. They are very soluble both in organic solvents (like alcohol, ether, and the fatty components of the body) and in water (aqueous solution), where they are strongly acidic. They exert toxic effects in the brain, where normally certain enzymes prevent their accumulation." Salicylates -- "Salicylate is a natural chemical made by many plants. It is chemically related to aspirin, which is a derivative of salicylic acid. It is believed the plant uses it as protection from insects. Although natural salicylates are found in wholesome foods, some individuals have difficulty tolerating even small amounts of them. The reaction to a natural salicylate can be as severe as that to synthetic additives if a person is highly sensitive. Some people are troubled by only one or two, while others are sensitive to all of them."
Here is a short list of high phenol foods, which you would want to eliminate or at least reduce to prevent overload, is food dyes, tomatoes, apples, peanuts, bananas, oranges, cocoa, red grapes, colored fruits, and milk.