Getting Sick Often: Frequent Infections and "Low Immunity"

Feeling like you are always sick

Many people ask why they get sick so often or whether they have a "weak" or "low" immune system. Those phrases are common in everyday speech and on product labels, but they are not diagnoses. This page explains what is normal, which patterns are worth checking, and why most frequent colds do not mean an immune disease.

What is normal

Colds are probably the most common illness. Adults average 2 to 3 colds a year, and children have more. More than 200 different viruses can cause a cold, so catching a new one is common. [1] Symptoms usually start a few days after infection, and some can last 10 to 14 days. [1] The NHS says you should begin to feel better in about 1 to 2 weeks. [2] So a run of colds in a season, especially with children at home or a busy workplace, is often within the normal range.

Things that can make illness more frequent

• Exposure. Colds spread through the air and by touching surfaces and then your eyes, mouth or nose. [1]
• Sleep. In an experiment with 164 healthy adults exposed to a cold virus, those sleeping under 5 hours or 5 to 6 hours were more likely to develop a cold than those sleeping over 7 hours. [3]
• Smoking and heavy alcohol use. See habits for immune health. [2][4]
• Mixing up conditions. A cold usually passes in 1 to 2 weeks, while hay fever can last weeks or months. [5] See allergies vs colds.
• Other health conditions or medicines. Some conditions and medicines weaken the immune system (see below).

"Low immunity" versus immunodeficiency

MedlinePlus describes immunodeficiency diseases as conditions where the immune response is reduced or absent. People with them get sick more often, and infections may last longer and be more serious and harder to treat. [6] A clinician might think about it if you have infections that keep coming back or do not go away, a severe infection from germs that do not usually cause severe illness, a poor response to infection treatment, or delayed or incomplete recovery. [7] Tests can include immunoglobulin levels, white blood cell counts and checking responses to vaccines. [7]

Notice the difference: feeling run-down after several ordinary colds is not the same as the pattern above. This page cannot tell you which applies to you. See immunodeficiency, autoimmune conditions and immunosuppression.

Causes of weakened immunity that are not inherited include HIV, malnutrition (especially not eating enough protein), some cancers, removal of the spleen, and medicines such as corticosteroids or chemotherapy. [7] Diabetes also raises the risk of certain infections. [7]

What may help

• Wash hands and cover coughs. [2][8]
• Keep vaccines up to date. [9] See vaccines and infection prevention.
• Look after sleep, activity and not smoking. See habits for immune health.
• Be cautious with "immune" supplements: the NHS says there is little evidence that vitamin C, echinacea or garlic prevent colds. [2] Details: vitamin C, vitamin D and zinc.

When to get help

Consider seeing a clinician if:

• infections keep coming back or do not go away [7]
• you often get sore throats (the NHS advises seeing a GP) [10]
• cold symptoms do not improve after 10 days, or you have a cough for more than 3 weeks [2]
• you get cold symptoms and have a long-term condition or a weakened immune system [2]

Urgent: sudden chest pain, severe difficulty breathing or coughing up blood need emergency care; use your local emergency number (911 in the US). [11] More in immune safety and when to get help. Keep a list of supplements to share with your clinician: talking with a health professional.