Some of these include phenolic compounds, sulphur dioxide and hydrocarbons. In cities, motor vehicle and industrial emissions are major sources of chemicals such as, sulphur dioxide, hydrocarbons, toluene diisocyanate, dioxins, furans, particulates, ozone and even heavy metals. In rural areas high usage of agricultural chemicals is a major source of airborne chemicals. While not all chemicals are sensitisers, some have other methods of action that cause health problems e.g. some are respiratory irritants, nerve poisons and carcinogens. The food we eat can contain agricultural chemical residues left over from best practice use, food additives, sulphur dioxide.
Packaging materials can leach into food and contribute to adverse reactions.
Food also contains naturally occurring chemicals such as salicylates, amines and nitrates that can contribute to sensitivity reactions. Water can contain agricultural chemical runoff, chlorine, other water disinfectant treatments, heavy metals. The same chemicals that are found outside are also found indoors. However, indoor air can be further contaminated by chemicals such as pesticides, plasticisers, or formaldehyde that is found in building products, furnishings, carpet, detergents, disinfectants, toiletries and many others. This is known as sick building syndrome.