The most likely cause is the convergence of large numbers of people arriving from all over the world. The poor diet and heavy consumption of alcohol during
freshers' week is also reported as a cause for many of the illnesses contracted during this time. "Stress, which may be induced by tiredness, combined with a poor diet, late nights and too much alcohol, can weaken the immune system and be a recipe for ill health. All this can make students and staff working with the students more susceptible to infections within their first weeks of term." In addition to this, nearly all university academic years in the UK commence around the end of September or beginning of October, which "marks the start of the annual flu season". The increased susceptibility to illness from late nights, heavy alcohol consumption and stress peaks 2–4 weeks after arrival at university and happens to coincide with the seasonal surge in the outbreaks of colds and flu in the
Northern Hemisphere. ==Other effects==