You hardly notice it, a little prick which leaves an irritating itch, possibly rash or minor inflammation. The symptoms usually disappear after a short while and are therefore regarded as nothing more that a unpleasant little nuisance. In most cases, there is nothing more to worry about. Nevertheless- in an increasing number of cases, people suffer far more unpleasant allergic reactions.
Not only that, insects can also transmit diseases. In the tropics, malaria, yellow fever and dengue fever are all a possibility, where as in more temperate climate, it's ticks who are the danger, carrying, amongst others, lyme disease (lyme borreliosis) and FSME (early summer meningo-encephalitis), a form of meningitis. Prophylaxis against insect bites therefore makes a major contribution to preventative medicine.