Sick again? What lies behind frequent colds

What does ‘susceptible to infection’ mean?

‘Susceptible to infection’ means that the body is particularly prone to catching infections. The immune system is therefore less able to fight off infections than average, and those who are susceptible to infection “catch every wave of colds”. Whilst other people might only catch a cold once a year, those who are susceptible to infection are affected much more frequently or more severely.

How many infections a year are normal?

Two, three or even four colds a year – is that still normal? Many people feel anxious when they fall ill several times a season. In fact, the frequency of infections depends heavily on age and lifestyle. A child’s immune system first needs to become familiar with many pathogens in order to build up resistance, whilst an adult’s immune system already has a well-stocked ‘database’.

For example, children who attend nursery or school may have infections very frequently, and this is completely normal, as it ‘trains’ the immune system. On average, adults suffer from two to four infections a year, which usually occur in autumn or winter. Older people, on the other hand, tend to have infections less frequently, but these are more likely to be severe.

External factors also play a role: anyone who has a lot of contact with children or regularly comes into contact with large numbers of people is more frequently exposed to pathogens. Having several infections during the autumn/winter season can therefore be normal – provided you are fully recovered in between.

It is important, however, to remain vigilant. It is advisable to seek medical advice if

• infections last for an unusually long time (e.g. a cold that does not clear up after three weeks).
• simple colds frequently develop into bacterial infections (e.g. sinusitis or pneumonia).
• you never feel properly fit and able to function between infections.

At what point does ‘being ill too often’ really become a cause for concern?

Not every cold is a cause for concern. However, if infections occur unusually frequently or are particularly severe, you should take notice. If one or more of the following warning signs apply, ‘too often’ is indeed a cause for concern:

• The number of infections: In adults, more than six to eight infections requiring treatment per year. In children, more than ten to twelve infections, particularly if these are unusually severe.
• The severity of complications: If a simple cold regularly develops into sinusitis, bronchitis or an ear infection.
• If two or more serious infections, such as pneumonia or meningitis, occur within a year.
• If the infections do not respond to standard treatments and long-term antibiotic therapy is required to bring about an improvement.
• In the case of infections caused by ‘atypical’ bacteria or harmless fungi, which a healthy immune system would normally fight off with ease.
• If you never feel completely well between infections and the symptoms drag on for weeks without any real recovery taking place.

Such signs should be investigated by a doctor in order to identify possible causes in good time.

Why do some people fall ill more often?

It is usually a combination of several factors. These include:

• Genetics and fitness: Some people naturally have fewer immune cells, whilst others have more antibodies due to previous exposure.
• Condition of the mucous membranes: Dry air, smoking or insufficient fluid intake make the barriers in the nose and throat more permeable to viruses.
• Lifestyle: Lack of sleep, chronic stress and nutrient deficiencies (particularly vitamin D, iron and zinc) can impair the immune system.
• Gut health: Around 80 per cent of the immune system is located in the gut. An imbalance in gut flora can weaken the entire immune system.
• Frequent exposure: People who work a lot with children or in crowded places are simply more prone to infections

Can being ill frequently be a sign of a serious illness?

Yes, it can be a warning sign, but in most cases the causes are easily treatable. Common reasons for recurrent infections, as described above, include lack of sleep, chronic stress or a nutrient deficiency.

In rare cases, however, serious underlying conditions may be to blame, such as undiagnosed diabetes, autoimmune diseases or chronic areas of inflammation.

You should seek medical advice if

• you experience more than eight to ten infections a year
• even a mild cold regularly leads to serious complications such as pneumonia.
• you also experience night sweats, unintentional weight loss or persistent fatigue.

A full blood count can often quickly determine whether there is an underlying cause that requires treatment.

What are common causes of frequent colds?

Typical causes of recurrent colds include:

• lack of sleep, chronic stress and too little exercise in the fresh air.
• A deficiency in key nutrients such as vitamin D, zinc, iron or vitamin C.
• Air that is too dry from central heating in winter: this irritates the nasal mucous membranes, making it easier for viruses to penetrate.
• Frequent contact with large numbers of people (e.g. children at nursery or school, open-plan offices).
• Chronic inflammation of the sinuses or problems with teeth or tonsils, which place a constant strain on the immune system.
• Allergies: Sometimes what you think is a ‘cold’ is actually an allergic reaction (e.g. to house dust mites).

When are a cough or a runny nose considered chronic?

Chronic cough

A cough is described as chronic if it lasts for more than eight weeks. If the cough lasts for up to three weeks as part of a viral infection, it is classified as an acute cough. A subacute cough often occurs as an after-effect of an infection and can last for three to eight weeks.

Chronic runny nose

The threshold here is usually more than twelve weeks. A runny nose is considered chronic if the nasal mucosa remains inflamed for over three months or if the symptoms (stuffy nose, runny nose) persist.

Please note: ‘Chronic’ means that the symptoms never disappear completely. If, in between, you are completely symptom-free for one to two weeks at a time, this is more likely to be a recurrent (recurring) infection – not a chronic cough or runny nose.

What often weakens the immune system?

Why is the immune system sometimes more vulnerable than usual? The immune system is often weakened by a combination of lifestyle and physical factors. These include:

Lifestyle and stress

• Chronic stress: Constant stress leads to increased cortisol release. This can suppress the activity of immune cells, making it easier for viruses to take hold.
• Lack of sleep: During sleep, the immune system produces important messenger substances. Anyone who regularly sleeps for less than six to seven hours weakens their immune system in the long term.

Diet and essential nutrients

• Nutrient deficiencies: The immune system requires certain building blocks to produce immune cells. Deficiencies in vitamin D, zinc, selenium and iron are particularly critical.
• Sugar: A high sugar intake can temporarily impair the ability of white blood cells to fight off bacteria.

Physical and environmental factors

• Dry mucous membranes: Dry air from central heating or insufficient fluid intake makes the protective barriers in the nose and throat more vulnerable.
• Gut health: Around 70 to 80 per cent of immune cells are located in the gut. An imbalance in gut flora (e.g. following a course of antibiotics or due to an unbalanced diet) can weaken the entire immune system.

Stimulants

• Alcohol: It can impair parts of the immune system for up to 24 hours after consumption.
• Smoking: It paralyses the cilia in the airways, which normally clear away mucus and pathogens.

Why do people get ill more often after having COVID-19?

Many people report that they have been more prone to colds since having COVID-19. Is this a coincidence, or is there more to it? In fact, there are several possible explanations. Studies show that the coronavirus can alter the composition and function of immune cells for months on end. Certain immune cells (T-cells) often appear ‘exhausted’ after infection, or their numbers are temporarily reduced. This is referred to as a kind of malfunction: the immune system remains in a state of overactivity or chronic inflammation, leaving fewer resources available to fight off new, mostly harmless cold viruses.

Another explanation suggests that a coronavirus infection can place such a heavy strain on the immune system that other viruses already present in the body become active again. This further weakens the immune system and increases susceptibility to new infections.
The microbiome also plays an important role, as a large part of the immune system is located in the gut. A COVID-19 infection can disrupt the balance of gut bacteria. If the gut is weakened, overall resistance to respiratory infections also decreases.

Finally, during the pandemic, the immune system had less contact with everyday viruses due to masks and social distancing rules. Now that these measures have been lifted, we are once again increasingly exposed to viruses against which we no longer have short-term immune protection.

Post-Covid

Post-Covid is complex, but can be broken down into three key points:

• Firstly, the immune system is under constant stress: the virus can keep the immune response trapped in a persistent inflammatory loop. This depletes the resources needed to defend against new infections.
• Secondly, the ‘cellular powerhouses’ (mitochondria) may have been impaired by the COVID-19 infection. This can lead to the typical fatigue and weakness experienced after physical exertion.
• Thirdly, circulatory problems may occur. Tiny clots can impair the oxygen supply to organs and immune cells.

Important: Experts recommend not ‘fighting’ the fatigue, as overexertion in post-Covid often leads to relapses. It is crucial to accept one’s own energy limits and give the body time to recover.

When should you see a doctor?

However, certain warning signs should be taken seriously and investigated by a doctor.
It is advisable to book a doctor’s appointment if

• cold symptoms persist for more than two weeks without improvement.
• Infections occur more than eight to ten times a year.
• Even harmless infections regularly lead to complications (e.g. pneumonia, sinusitis or the need for antibiotics).
• In addition to a cough and a runny nose, you experience a fever above 39 °C, unintentional weight loss, severe night sweats or persistently swollen lymph nodes.
• This leads to extreme exhaustion (fatigue), which worsens significantly even after minimal exertion.

5 tips – How to strengthen your immune system in the long term

A strong immune system doesn’t develop overnight, but you can actively help build it up. These five measures will support your defences in the long term:

• Check your nutrient intake: Vitamin D (particularly in winter), zinc, selenium and iron are key building blocks for the immune system.
• Promote gut health: A large proportion of immune cells are located in the gut. Fibre (prebiotics) and fermented foods such as yoghurt or sauerkraut (probiotics) can support the gut flora.
• Reduce stress: Chronic stress weakens the body’s defences. Make a conscious effort to schedule periods of rest – especially after a bout of COVID-19.
• Get enough sleep: Seven to eight hours of restful sleep per night help the immune system to regenerate.
• Protect your mucous membranes: Drinking enough fluids (around two litres a day) and maintaining good humidity levels help keep your airways more resistant to viruses.