The World Health Organisation takes noise seriously. On its website, together with such health afflictions as Aids, brucellosis, cancer and dysentery, it also lists noise.

That noise is a nuisance and an annoyance, we all know. Our lives are lived in an environment of community noise, also known as environmental, residential or domestic noise.

The main indoor sources are fans and air-conditioners, office machines, home appliances and neighbours. Other typical sources of neighbourhood noise include the catering trade (restaurants, cafeterias and street hawkers), live or recorded music, sports, playgrounds, car parks, barking dogs, temple fairs.

These noises irritate and make us tense by day, keep us awake at night so that by next day we are even more irritable and upset. It becomes more difficult to concentrate attention at work or school. Noise affects social behaviour, giving rise to aggressiveness, protests and feelings of helplessness. Noise makes speech difficult, we strain to communicate with and to hear others.

While such experience does lead to health problems, the WHO insists that noise itself is a direct health hazard - such as the pain and hearing fatigue we suffer from noise, and more seriously, hearing impairment and tinnitus which may be irreversible and permanent.

Sleep disturbance with all its consequences on a long- and short-term basis are a grave health problem. Either directly from noise, or through its interference with normal bodily function, cardiovascular effects follow; high blood pressure is a well-identified accompaniment of continual exposure to noise; there are also hormonal responses to the ensuing stress, with possible consequences on human metabolism and the immune system.

Most of the threats listed hardly need explanation; we are only too familiar with them in our daily lives. But what may surprise is the prevalence throughout the world of the excessive level of these threats.

The WHO estimates that, globally, some 120 million people are estimated to have disabling hearing difficulties. More than half the citizens of Europe live in noisy surroundings; a third experience levels of noise at night that disturb sleep.

In the US, in 1990 about 30 million people were exposed to a daily occupational noise level above 85 decibels, compared with more than nine million people in 1981; these people were mostly in the production and manufacturing industries.

In Germany and other developed countries as many as 4-5 million, that is 12-15% of all employed people, are exposed to noise levels of 85dB or more. In Germany, an acquired noise-related hearing impairment that results in 20% or more reduction in earning ability is compensatable; in 1993, nearly 12,500 new such cases were registered.

Prolonged or excessive exposure to noise, whether in the community or at work, can cause permanent medical conditions, such as hypertension and ischaemic heart disease. Noise can adversely affect performance, for example in reading, attentiveness, problem solving and memory. Deficits in performance can lead to accidents. Noise above 80dB may increase aggressive behaviour.

A link between community noise and mental health problems is suggested by the demand for tranquillisers and sleeping pills, the incidence of psychiatric symptoms and the number of admissions to mental hospitals. To reveal the serious nature of noise problems, one can hardly do better than reproduce these data on the ill effects of noise attested to by the WHO.

In a final article in this series on noise, serious sources of noise disturbance in Bangkok itself will be identified. But it is useful first to examine more closely some of the health hazards identified above.

Our schooling in the meaning of decibels is now necessary to assess the danger. Sleep disturbance is one of the most obvious and serious effects of environmental noise. WHO guidelines say that for good sleep, sound levels should not exceed 30dB(A) for continuous background noise, and individual noise events exceeding 45dB(A) should be avoided.

Well, and what happens if our sleep is disturbed? The WHO ominously indicates consequences on a long- and short-term basis. The short-term effects are clear enough: next day we feel tired. Our social interactions with others are impaired, our attention wanders, we become irritable and can hardly study or concentrate on tasks. If the cycle repeats our state grows worse, and the longer-term effects appear. But this development and its severity is not the same for everyone. Not all smokers get lung cancer, not all heavy drinkers suffer cirrhosis. There is a range of vulnerability which seems especially relevant in noise effects where deterioration in hearing and development of serious long-term effects may be rapid in some persons but gradual in others. The impairment in hearing due to a noisy workplace, or use of ipod earphones with too high an amplification setting, lessens our ability to detect the deterioration. The hearer easily comes to believe that he or she is the exception who will not be affected, or may even think, well, so what, if I become a little hard of hearing I can always increase the volume! Sometimes, the effect of the damage is only realised years later when it is far too late to remedy it. One-time artillery gunners, orchestra players, telephone operators are among those who discover in later life that they are seriously disabled by damaged hearing and can only turn to legal action for compensation. In the case of young people using hearing devices, widespread damage to hearing has been registered in whole populations.

Long-term effects of noise are said to include high blood pressure and heart disease. However, doctors are slow to say that this or that case of high blood pressure are due to noise. We all know that high blood pressure can be caused by multiple factors. In the list of noise effects taken from the World Health reports, we find the telltale phrases: "exposure to noise... can cause permanent medical conditions", "Noise can adversely affect performance", "Noise... may increase aggressive behaviour". And so on.

Now, doctors are canny creatures and there is enough of science in the art of medicine to stop them saying outright that effect follows cause. But that is the nature of noise and its effects, accidents and bodily injury, infection and disease. Insurance companies base their business on the link of effect to cause, which, ruled by statistical law, is just as sure as the link between death and jumping off a 10-storey building.

One of the most compelling links between noise and illness was published only a month ago. Called the HYENA Report, it relates to a study of 4,861 persons who have lived for at least 5 years near one of six major European airports. The study collected detailed data on the subjects and found significant excess risk of high blood pressure related to long-term noise exposure, primarily for night-time aircraft noise and daily average road traffic noise. High blood pressure is an important risk factor for cardiovascular disease and even a small contribution in risk may have a major impact on public health. The report is detailed and technical, the result is clear: excessive noise kills. At the very least it impairs lives.

Tinnitus, an affliction where the sufferer hears continuous phantom noise, is caused by exposure to actual noise and is becoming widespread. It may be transitory, such as suffered by a musician for about three hours after a performance. Or it may become permanent It is truly a torturous experience. Tinnitus, like most ill-health effects of noise, may be alleviated but has no direct medical cure. The only measure available is to reduce noise levels to protect further aggravation and symptoms and to protect a future generation. The remedy must come from ourselves and an authority which enforces limitations on noise levels.

Danthong Breen is Chairman of the Union for Civil Liberty in Bangkok.