D. Chronic effects

Some hazardous substances cause chronic effects, which usually appear a long time after the exposure occurred and persist over time. A chronic condition usually only appears after a long time because of the disease's latency period (the period of time between the exposure and the first sign of disease). Chronic conditions, such as many occupational cancers, may take 20 or 30 years to develop.

Some chronic conditions develop after just a short exposure, whereas other chronic conditions only develop after repeated contact with a substance or work process.

Like acute effects, chronic effects can be localized to one part of the body (such as chronic lung disease which develops over years), but they can also be systemic.

For all diseases, it is better to prevent rather than treat the illness once it has developed, but for chronic diseases such as cancer, prevention is the only cure. With chronic diseases it is difficult to establish the cause of the condition and even harder to get compensation. Thus it is important to document all exposures to workers and maintain good records for at least 30 years.

Can exposure to some hazards cause both acute and chronic effects?

While exposure to some hazards only causes either an acute or a chronic response, exposure to other hazards - such as formaldehyde and noise - can cause both kinds of effects. Short-term exposure to formaldehyde may cause headaches or eye irritation (acute effects), while long-term exposure may cause recurring allergic skin reactions or cancer (chronic effects). Short-term exposure to loud noise may cause ringing in the ears, while long-term exposure may cause permanent hearing loss. Solvents can also produce both acute and chronic effects on the nervous system.

Local, systemic, acute and chronic health effects can all result from exposure to one substance. For example, if a worker drinks too much alcohol, these are the possible effects that can result:

· Local effects - stomach irritation and stomach upset.

· Systemic effects - an increase in the blood alcohol level, which can cause damage to brain cells.

· Acute effects - drunkenness, headache and a hangover.

· Chronic effects - permanent liver damage, which can have a latency period of many years.