Weak immunity makes the body more susceptible to disease and infections. Some weak immunity causes are well known, while others are more surprising.

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Surprising Things that Cause a Weak Immune System

Spending Too Much Time Indoors

During winter months, people typically spend more time indoors and wear clothing that covers more skin. This may weaken immunity and cause more infections during colder months.

The body requires vitamin D for a strong immune system. Vitamin D signals the body to produce antibodies and influences immune responses.

Cells in the skin synthesize vitamin D when exposed to natural sunlight. Spending too much time indoors and covered up prevents this process, which may lead to vitamin D deficiency and a weak immune system.

Pathogens thrive in overcrowded environments. This is another reason why weak immunity is more prevalent in winter.

Spending a lot of time in enclosed areas with poor ventilation increases exposure to pathogens. As a result, the immune system becomes more susceptible to infection.

Physical Activity

A sedentary lifestyle has been linked to numerous health issues like inflammation, chronic diseases, and impaired immune function. An active lifestyle seems to have the opposite effect on health.

A recent study found exercise may increase gut microbiome diversity. More diversity reduces the risk of infection and improves the immune system.

On the other hand, too much exercise may compromise the immune system. Many physiological systems are affected by overtraining, but the immune system is particularly vulnerable.

Overtraining syndrome mostly affects athletes.


Nicotine from smoking increases cortisol levels while inhibiting the immune system. Smoking reduces antibody formation and lowers immune cell response to antigens.

According to a study published in PLOS One, vapor from e-cigarettes could damage the lungs, making them vulnerable to infection. The vapor from e-cigarettes also contains free radicals, which cause inflammation and weaken the body’s response to pathogens.

Smoking has also been associated with a decrease in beneficial gut bacteria. The immune system heavily relies on the gut, and less diversity in the gut results in a weakened immune response.


People who abuse alcohol are at higher risk of infection because alcohol inhibits the process of attacking pathogens.

Alcohol gets broken down into acetaldehyde in the liver. Acetaldehyde weakens ciliary function in the lungs. This makes them more susceptible to bacterial and viral attacks.

Heavy drinking can lead to a bacterial imbalance and inflammation of the gut. Chronic inflammation may weaken the intestinal walls and cause toxins to leak into the bloodstream.

Alcohol also makes the immune system less effective because it impairs communication between beneficial bacteria and immune cells.

Poor Diet

It should come as no surprise that diet influences immunity. Obesity is linked to various adverse side effects such as cardiovascular disease, diabetes, and impaired immune response.

Unhealthy diets reduce the number of white blood cells. White blood cells form part of the immune response.

Aim for a variety of fruits and vegetables to support immune function.

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UV Radiation

According to the Environmental Protection Agency (EPA), increased air pollutants increase the level of harmful UV radiation.

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UV exposure weakens the immune system and affects the cells responsible for the immune response. This not only lowers the body’s defense against infection but also increases the possibility of developing skin cancer.

Protect your skin and immune system by applying sunscreen and wearing protective clothing.

Artificial Light

Artificial light affects the body’s sleep/wake cycle and may lead to poor quality sleep. Deep restorative sleep is necessary for a healthy immune system.

Furthermore, light from a computer screen or smartphone delays the release of melatonin. Melatonin protects the immune system and may regulate cellular and humoral immunity.

Melatonin also effectively combats viral and bacterial infections.

Temperature Changes

Temperature changes don’t cause infection, but it makes the body more vulnerable to viral and bacterial attacks. 

Some viruses like the rhinovirus, responsible for the common cold, replicate better in temperatures lower than body temperature. During colder temperatures, the inside of the nasal cavity, at approximately 91.4°F, is the perfect environment for rhinoviruses to thrive.

Researchers found another link between cold temperatures and immunity in 2015. 

To conserve heat during cold weather, blood vessels dilate. This seems to inhibit white blood cells from moving around the body, especially the lungs. 

White blood cells fight infection, and the restricted movement of these cells reduces the immune response.


Stress produces the hormone cortisol, which may improve short-term immune function. Extended periods with elevated cortisol levels, however, negatively impact immune response.

High cortisol levels suppress the T-cell function, a vital part of the body’s immune response. It may also lead to unhealthy coping methods like smoking, drinking, and unhealthy eating.

When the brain triggers a stress response, heart rate increases, and you become more focused on the immediate environment. To achieve this, the body diverts resources away from non-essential functions.

This puts a strain on the circulatory system and digestive systems.

Constant strain on the body and being stressed weakens not only your immune system but also increases recovery time after infection.


Isolation and loneliness may affect your immunity. It also puts you at risk of developing mental health problems like depression.

Isolation causes stress and anxiety. Increased anxiety is linked to free radicals.

Free radicals damage cells, leading to a weak immune system, premature aging, and even cancer.

Some physical contact or a video call can offer a reduction of stress and immune system support during social distancing.


Like stress, a sudden tragic event increases the cortisol levels in the body. The increased production of cortisol and other hormones causes weak defense against infection.

During periods of grief, certain vaccines, like the flu vaccine, are less effective.

Unexpected weak immune system causes can impair health and make the body more susceptible to disease. Though some causes are more common than others, it is essential to be aware of contributing factors. This ensures that you can counteract the causes when possible and boost your immune system when necessary.

Know any other ways to sleep better? Let us know in the comments below!

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