Absorption and injection are two routes of entry that occur through direct skin contact with a hazardous material.
Chemicals and hazardous substances may enter the body by several routes, and the nature and onset of signs and symptoms may vary accordingly. Gases, vapors, and aerosols, when inhaled, may be absorbed through any part of the respiratory tract, from the mucosa of the nose and mouth to the alveoli of the lungs. The eye may also directly absorb them. Aerosol particles larger than 5 micrometer (μm) tend to be retained in the upper respiratory tract, while those smaller than 1 µm tend to be breathed in and out again, although some of these smaller particles may be retained. Droplets of liquid and, less commonly, solid particles may be absorbed through the surface of the skin and mucous membranes. Toxic compounds with a characteristic action on the skin can produce their effects when deposited on the skin as solid or liquid particles.
Chemicals or hazardous substances which penetrate the skin may form temporary reservoirs so that delayed absorption may occur. Even the vapor of some volatile chemicals and agents can penetrate the intact skin and intoxication may follow. Wounds or abrasions (even minor injuries caused by shaving or by chemical depilation) present areas which are more permeable than intact skin. Chemicals and hazardous substances may contaminate food and drink and so be absorbed by the gastrointestinal tract. The penetration of chemicals and hazardous substances by these various routes may not be accompanied by irritation or damage to the surfaces concerned.
Methods of exposure to these chemicals are called routes of entry. They are:
- Absorption
- Ingestion
- Injection
- Inhalation