There are a few other causes for a weak immune system in adults; certain illnesses such as cancer, HIV, viral hepatitis, malnutrition, some medications and several medical treatments can cause a weak immune system. Children can also have certain illnesses that cause a weak immune system. Primary Immune Deficiency also known as PID is a hereditary condition that a relatively small number of children are born with. Children often become sick with bugs, colds and infections because their immune systems have not built up natural immunity like adults have done over the years. But, a weak immune system in children can also be caused by lifestyle factors including lack of sleep, poor nutrition and stress.

There are numerous myths about what causes a weak immune system, thanks in part to old wives’ tales being passed down from generation to generation over the years. Your child's immune system can be temporarily weakened by certain drugs, such as chemotherapy or other drugs used to treat cancer, or medication to prevent organ rejection following transplant. Also, infections like the flu virus, mononucleosis (mono) and measles can weaken the immune system for a brief time. If you want to know more details I would recommend checking out what causes a weak immune system in children.

Does sugar lower your immune system?
Sugar does lower your immune system because it reduces the number of immune system cells that attack harmful bacteria. This lasts for several hours after eating sugary snacks and desserts or after drinking sugary drinks.

Does your period weaken your immune system?
When women are ovulating, the body’s increased levels of progesterone suppress the immune system function to protect eggs in case they become fertilized and develop into a pregnancy, which means that females are more likely to become ill before their period.

Does a cold weaken your immune system?
The common cold can be caused by over 200 different types of viruses and comes with a distinct set of symptoms, including a cough, running nose and sneezing. It doesn’t weaken your immune system and many experts claim that exposure to many different types of colds is a good thing as it helps build up immunity, but if you're stressed and not sleeping or eating properly while unwell with a cold that could potentially weaken your immunity.

Does your immune system weaken with age?
While it is generally accepted that the very elderly have weakened immunity, studies have shown that immunity declines from the age of 35 onwards. As we age, the immune response becomes less efficient, mainly because there is a fall in the production of new lymphocytes (immune cells designed to detect, identify and destroy pathogens) and in the function of existing lymphocytes.

If immune cells are not recognizing or are misidentifying (autoimmune responses) then there is a greater chance of pathogens escaping notice instead of getting destroyed. This decline is exacerbated by inflammation, another process that increases as we age and contributes to aging. The persistent low-grade attack from chronic inflammation is a characteristic of most degenerative diseases and accelerates aging.