It is true that we can be 'under the weather'. Weather has short and long term effects on our bodies and this is studied by scientists called biometeorologists. It affects the death rate and is linked to seasonal illnesses such as winter flu, sunstroke, or hayfever. Some people claim that they can feel changes in the weather with aches and pains worsening and the onset of headaches. Some sufferers of rheumatism or arthritis even notice changes in atmospheric pressure affecting the fluid around their joints.

Our bodies react differently to the weather depending on our age, sex, or general state of health as well as where we actually live. These reactions are linked to our endocrine system, the system of glands which regulates the production of hormones in our bodies, and which is affected by pain, stress and the weather. One in three people are thought to be sensitive to the changing weather but the old, young and the chronically ill suffer more, and women are generally more sensitive than men.

To protect itself from too much heat or cold the body sweats or shivers. When we sweat, perspiration evaporates from the skin and cools you down. When we shiver muscles twitch and give off heat. In extreme heat our heart rate rises, blood vessels expand to let more blood reach the skin's surface (blushing helps us to cool down) and we sweat more. This can cause fainting, sunstroke and rashes, but the combination of dehydration and loss of blood from the central nervous system can lead to collapse. Elderly people are most affected by the heat but many young men drown each year trying to cool off with a swim or a paddle. The contrast between a high body temperature and the cold water can cause cramp especially if people swim after eating or drinking. In extreme cold our bodies react by closing blood vessels to keep the blood away from the skin and retain heat. However, for old people with poor circulation this can lead to a cycle of falling body temperature, inactivity, a further fall in body temperature and eventually death. Every winter the death rate rises because of this hypothermia, but other illnesses such as winter colds and flu can develop into pneumonia and bronchitis which can be very dangerous for those who are fragile. See weather dangers for more about the affects of extreme heat and cold.

Hayfever is an allergy to airborne pollen grains and it is at its worst during the early summer - exam period for schoolchildren and students who often rely on anti-histamine drugs to help them manage its ill-effects such as itchy eyes and dripping nose. Air pollution especially affects people with chronic lung diseases such as asthma and bronchitis. The famous London smogs killed thousands of people when smoke from factories and house fires converted ordinary fog into lethal smog. These only stopped after the Clean Air Act of 1956 which outlawed smoke from coal fired chimneys. Today a new form of smog caused mainly by traffic exhaust emissions is giving us problems with air quality in some areas. You can look up a Pollution Index and a Pollen Index on this site.

The ultra violet (UV) rays of the sun can cause the skin to burn if unprotected. Habitual sun-worshippers are most at risk, but even a single over-exposure to UV rays can permanently damage the skin. Fair-skinned people tend to get sunburnt more easily than people with darker skin which contains a lot of melanin, a brown pigment which acts as a shield against the harmful rays. There has been a dramatic increase in skin cancers, with cases of the most lethal, melanoma, doubling every ten years. Now that we are aware of the link between sun damage and skin cancers we can protect ourselves by using sunscreen creams. However we also have to be aware that the effect of the sun's rays increases according to the height and strength of the sun and in some parts of the world the ozone layer has been partially depleted allowing more of the harmful UV rays to get through. The Sun Index measures this and can be found on this site.

Sunshine is good for us in small quantities and is needed by our bodies to make vitamin D which is important for healthy growth. Too little sunshine can cause rickets which occurs when a lack of vitamin D prevents the bones growing properly. This was common in Victorian times but has been virtually eradicated in the UK because of healthier diets and greater exposure to sunlight.

Different weather has benefits for health, and climatotherapy is the idea of recommending different weather conditions for different illnesses. Patients with tuberculosis or blood diseases were often sent to mountain resorts with their lower levels of water vapour and higher ozone levels. Seaside resorts were considered to be good for the health with the sea air being rich in sodium and iodine vital for the healthy functioning of the body. The seaside climate is also recommended for those suffering from such chronic illnesses as bronchitis and rheumatism. In some cases we create an artifical environment by using ionisers, air conditioning or humidifiers. This can be bad for the health too and bad air conditioning systems have been blamed for Sick Building Syndrome in which increased concentrations of germs, bacteria and other pollutants like cigarette smoke cause a wide variety of health complaints.