Why Do I Keep Getting Colds?

It is one of the most common things patients tell me in autumn: "I have only just got over one cold and now I have another one." Sometimes it really is one cold after another. Sometimes it is one long cold with a lull in the middle. And sometimes it is not a cold at all. Working out which is the first step.

How many colds is normal?

Most healthy adults get two to four colds a year, each lasting seven to ten days, with a cough that can linger for three weeks. Children under five catch six to ten a year, and parents of young children or anyone who works with them catch a good share of those. Between October and March a cold roughly every four to six weeks is unremarkable. What is not normal is a cold that reliably turns into something that needs antibiotics, or infections that spread to the chest, sinuses or ears again and again.

The ordinary reasons you keep catching colds

You are being exposed more than you were

A new baby at nursery, a new job in a busy office, a long commute by train, a return to the gym: all of these multiply the number of viruses you meet. There are more than 200 viruses that cause the common cold and immunity to one does not protect you from the next.

Short sleep

Sleep is the strongest everyday factor. In controlled studies, people sleeping under six hours a night were about four times more likely to develop a cold after exposure to the virus than those sleeping over seven. Shift work, a new baby and late screens all count.

Stress

Prolonged stress raises cortisol, which dampens the immune response and makes both catching a cold and a longer recovery more likely. It also tends to go hand in hand with poorer sleep, more alcohol and less exercise.

Smoking, vaping and alcohol

Smoking damages the cilia that sweep viruses out of the airways, and smokers catch more colds and have worse chest symptoms. Early evidence suggests vaping does similar things to the airway lining. Regular alcohol above the recommended 14 units a week also blunts immune function.

Low vitamin D

Vitamin D is involved in the immune response in the airway, and levels in the UK drop sharply between October and April because there is not enough sunlight to make it. Trials show that correcting a deficiency reduces respiratory infections, most clearly in people who start out very low. It is one of the few causes on this list that a blood test can confirm and a supplement can fix.

Iron deficiency

Low iron, with or without anaemia, is common in women with heavy periods, in vegetarians and vegans, and in anyone with a poor diet or gut condition. It causes tiredness that is easy to blame on colds, and it impairs immune cell function. A ferritin test answers it.

Diabetes and thyroid problems

Poorly controlled or undiagnosed type 2 diabetes raises infection risk, and an underactive thyroid causes the fatigue and low mood that make every cold feel heavier. Both are picked up with simple blood tests.

Things that look like repeated colds but are not

• Allergic rhinitis (hay fever, or year round allergy to dust mite, pets or mould): a blocked, runny, itchy nose and sneezing that lasts for weeks, no fever, no sore throat, often worse in the morning or in particular rooms. Very commonly mistaken for an endless cold.
• Chronic sinusitis: facial pressure, thick discharge and a blocked nose for more than 12 weeks, often with loss of smell.
• Post viral cough: a cough that lingers for three to eight weeks after one cold, which can feel like a new cold starting.
• Asthma: wheeze, chest tightness and a night time cough that flares with every cold and takes longer to settle.
• Acid reflux: a dry cough, throat clearing and hoarseness, especially lying down, with no cold symptoms at all.

If your "colds" never come with a fever or a sore throat and last more than ten days at a time, one of these is more likely than a virus.

When repeated infections point to an immune problem

Genuine immune deficiency in adults is uncommon, but it exists and it is treatable, so it should not be missed. The pattern is different from ordinary colds. Warning signs include:

• Two or more courses of antibiotics a year for chest, sinus or ear infections
• Pneumonia, or an infection that needed hospital treatment
• Infections that keep coming back in the same place, or in unusual places such as the skin or bone
• Colds that routinely last three weeks or more with thick green or yellow discharge
• Infections alongside unexplained weight loss, night sweats, swollen glands or persistent diarrhoea
• A family history of immune deficiency

The commonest adult cause is antibody deficiency (for example common variable immunodeficiency), which is diagnosed with an immunoglobulin blood test and treated with replacement antibodies. Other causes include medicines that suppress the immune system, including long term steroids, some rheumatology and dermatology drugs, and chemotherapy, and conditions such as HIV, myeloma and lymphoma. Anyone with the pattern above should have a proper assessment rather than another decongestant.

Which blood tests are worth doing?

For someone who feels they are catching everything, a short panel answers most of the questions in one visit:

What actually reduces the number of colds

Vitamin C, zinc lozenges and echinacea have been studied extensively. Zinc started within 24 hours may shorten a cold by about a day; vitamin C taken regularly slightly shortens colds in some people but does not prevent them; echinacea has no consistent effect.

When to see a doctor

Book an appointment if you have had two or more infections needing antibiotics in a year, a cold that has lasted more than three weeks, a high fever that is not settling, chest pain or breathlessness, or any of the red flags above. It is also worth a consultation if your "colds" never come with a fever, because treating an allergy or reflux properly can end months of symptoms.

Questions people ask

Is it normal to get a cold every month?

In winter, for an adult around young children or in a crowded workplace, a cold every four to six weeks is within the normal range. Outside winter, or if each cold lasts more than ten days or needs antibiotics, it is worth looking for a cause. Also check that the symptoms are really a cold: allergy, sinusitis and reflux all produce cold like symptoms that never fully clear.

Can a weak immune system cause constant colds?

Yes, but true immune deficiency is rare and it tends to cause infections that are severe, unusual or need repeated antibiotics, not just frequent mild colds. The commonest treatable cause in adults is antibody deficiency, found with an immunoglobulin blood test. Far more often the explanation is sleep, stress, exposure, smoking or a vitamin D or iron deficiency.

What vitamin deficiency causes frequent colds?

Vitamin D deficiency is the one with the best evidence, especially in the UK between October and April. Iron deficiency also impairs immune function and causes the fatigue that makes colds feel worse. Zinc deficiency is uncommon in the UK but can occur with a poor diet or gut disease. All three are measured with a blood test.

Why do I keep getting colds but my partner does not?

Exposure and sleep usually explain it. Whoever does more of the school run, commutes on public transport or works with the public meets more viruses. Short sleep, stress, smoking and a low vitamin D or ferritin all make one person more susceptible than another in the same house.

Which blood tests check for frequent infections?

A full blood count, ferritin, vitamin D, HbA1c and thyroid function cover the common causes. If you have the warning signs of immune deficiency, immunoglobulins and an HIV test are added. At OneMedicine these can all be taken from one sample, with a GP reviewing the results.

Does vitamin C stop colds?

Not for most people. Regular vitamin C slightly shortens colds and reduces their severity, and it does prevent colds in people under extreme physical stress such as marathon runners, but taking it once a cold has started makes no difference. Zinc lozenges within the first day may shorten a cold by about a day.

Can stress make you catch more colds?

Yes. Long term stress raises cortisol, which suppresses the immune response, and it usually comes with worse sleep and more alcohol. In exposure studies, people under chronic stress were roughly twice as likely to develop a cold after contact with the virus.

Written by Dr Ibrar Ahmed, MBChB MRCP MRCGP PhD PG Dip (Cardiology), GMC 4401399
Specialist interest: Cardiovascular Medicine · OneMedicine, CQC registered clinic