Why do people in the UK get ill so often in autumn, and is it really just seasonal?

September arrives. Children return to school, colleagues go back to the office, and within a few weeks, people everywhere seem to be coughing, sneezing and complaining of sore throats. The same thing happens every year.

Many people describe this as “seasonality”, as though autumn itself were the cause. Science, however, presents a more complex explanation.

Are viruses really more active in autumn?

Partly. Some viruses, particularly rhinoviruses, which cause a large proportion of common colds, survive and spread more effectively in colder, drier conditions. Influenza also follows a seasonal pattern. However, this explains only part of the situation.

A more important question is why our immune systems find it harder to deal with these viruses specifically during autumn. The answer lies not only in viral activity but also in the changes that take place in the human body during the transition between seasons.

Six real reasons people in the UK get ill more often in autumn

1. Falling vitamin D levels

This is probably one of the most important and best-documented factors. During summer, the body can produce vitamin D in the skin through exposure to sunlight. By September, the angle of the sun becomes lower and vitamin D production through the skin becomes considerably less effective.

Vitamin D is not simply a “bone vitamin”. It also helps regulate cells of the immune system, including T lymphocytes and macrophages. When vitamin D levels fall, the immune system’s ability to recognise and respond to viruses may be affected.

Vitamin D deficiency is common in the UK during autumn and winter, including among people who spent plenty of time outdoors during summer.

2. Changes in sleep and disruption of the circadian rhythm

The days become noticeably shorter in September and throughout autumn. This may sound like a minor fact, but biologically it can place additional strain on the body.

The circadian rhythm, or the body’s internal biological clock, is mainly synchronised by light. When the amount of daylight decreases rapidly, the body must adapt, and that adjustment can take several weeks.

During this period, sleep may become less deep, waking times may no longer correspond with the body’s biological morning, and melatonin production may change. Sleep is also one of the most important regulators of the immune system. During deep sleep, the body produces cytokines that play a role in fighting infections.

People who sleep for around six hours may be considerably more susceptible to colds than those who regularly sleep for seven to eight hours.

For this reason, the sleep environment in autumn is not only a matter of comfort but also of health. Breathable bedding made from natural materials such as percale, Tencel or cotton helps the body maintain a comfortable temperature during the night and creates better conditions for uninterrupted sleep. You can find this type of bedding in the SAVAS Home collection.

3. Children returning to school – an efficient network for spreading viruses

Most parents recognise this from experience. Schools and nurseries are environments where infections can spread particularly effectively.

Hundreds of children spend time together indoors, touch numerous shared surfaces and then bring viruses home to parents, grandparents and siblings.

September is therefore not only the start of a new school year. It can also mark the beginning of a wave of infections that spreads from schools and nurseries to workplaces and homes within two or three weeks.

4. Returning to enclosed spaces

During summer, we spend more time outdoors. In autumn, we return to offices, schools, shops, public transport and other enclosed spaces.

A crowded and poorly ventilated room provides favourable conditions for viruses to spread. Aerosols may remain in the air for longer, close contact becomes more frequent and ventilation is not always sufficient.

Schools, offices and residential buildings in the UK are not always ventilated adequately. The COVID-19 pandemic drew greater attention to this issue, but it did not permanently resolve it everywhere.

5. Stress and suppression of the immune system

September can be one of the more stressful periods of the year for many people in the UK. Children return to school, workloads increase after summer holidays, deadlines approach and the days become shorter.

Chronic stress can affect the immune system partly through the action of cortisol. Cortisol is necessary for the body’s short-term response to stress, but consistently elevated levels may reduce the production and activity of certain immune cells.

This means that during autumn, many people are both more exposed to viruses and less well equipped to fight them off.

6. Changes in the indoor and sleep environment

This factor is discussed relatively rarely, even though it can have a direct effect.

As heating is used more frequently in homes, schools and offices, indoor air becomes drier. Relative humidity can fall to approximately 20–30%, while a level of around 40–60% is generally considered more comfortable.

Dry air dries out the mucous membranes in the nose and throat. These membranes are among the body’s first lines of defence against viruses. When they become dry, their protective function may be weakened. Under certain conditions, virus-containing aerosols can also remain suspended for longer in dry air.

Can it be prevented? What science suggests

There is no single solution, but several measures may help reduce the risk of infection and support the body during autumn.

Vitamin D

During autumn, it may be worthwhile to consider having your vitamin D level checked and taking a supplement when appropriate. A daily amount of 1,000–2,000 international units is often mentioned for adults, although the exact dose should be discussed with a doctor or another qualified healthcare professional.

Sleep quality

Good sleep is not a luxury. It is an important part of a properly functioning immune system. During sleep, the body carries out processes that support recovery and help it respond to infection.

Improving the sleep environment through a suitable temperature, darkness and appropriate bedding can directly influence sleep quality. Breathable bedding made from natural materials by SAVAS Home helps maintain a comfortable body temperature throughout the night and creates better conditions for deep, uninterrupted sleep.

A humidifier

A humidifier can be a worthwhile investment during the heating season. Maintaining bedroom humidity at approximately 45–55% can help the mucous membranes retain their natural moisture and continue performing their protective role.

Physical activity

Regular, moderate-intensity physical activity supports the body’s general resilience. Excessively intense exercise without sufficient recovery can have the opposite effect, so balance is important.

Hand hygiene

It may sound obvious, but regular handwashing remains one of the most effective ways to reduce the spread of infections. It is especially important after using public transport, before eating and after contact with someone who is unwell.

When should you contact a doctor?

Many autumn illnesses are viral and resolve on their own within seven to ten days. However, medical advice should be sought if:

• your temperature exceeds 39 °C and does not come down for more than two days;
• your symptoms continue for longer than two weeks;
• you develop a severe sore throat without a cough, as this may indicate a bacterial infection;
• you belong to a higher-risk group, such as older adults, people with chronic medical conditions or pregnant women.

In summary

Autumn itself does not cause illness. Instead, several circumstances occur at the same time, weakening the body’s defences while increasing exposure to viruses.

Falling vitamin D levels, changes in sleep, stress, dry indoor air and spending more time with other people in enclosed spaces all work together.

The good news is that many of these factors can be managed. Better-quality sleep, appropriate indoor humidity and attention to vitamin D levels may often provide more benefit than advertised products promising to “boost the immune system”.