5. Too much noise.
Everyone has his/her personal noise tolerance. If you find yours is getting lower all the time, it’s a sign that your immune system is fighting the intruder. Excess noise induces stress and we’ve already seen what that can do. Do what you can to reduce noise levels and volume—even introduce quiet hours at home. Heavy curtains can keep out external noise, white or pink noise can drown out unwelcome sounds, and turning off electronic devices (!) can all help reduce stress on your ears and hence your immune system.
6. Too much alone time.
Everyone needs time alone, but not enough social interaction can lead to an emotional, then physical, depressive response. Keep in touch with your friends and make new ones. Even if very shy, there are social outlets for everyone, whether a small monthly book club, a dance class, drop-in basketball, or a history course at the community college.
7. Not enough sleep.
Your body uses the time while you’re sleeping to do complete and thorough maintenance. If you don’t get enough, corners are cut that can affect your ability to keep healthy. Lack of sleep has the same effect on the immune system as stress and chronic sleep loss has implications for disease and immune function. According to a study by scientists in the United Kingdom and the Netherlands:
“Previous studies have associated sleep restriction and sleep deprivation with the development of diseases like obesity, diabetes and hypertension. Others have shown that sleep helps sustain the functioning of the immune system, and that chronic sleep loss is a risk factor for immune system impairment.” 
8. Depression and grief.
Chronic depression and/or extended grief affect the production of white blood cells that are specialized to kill damaged or infected cells. Many studies have found a direct correlation between depression and disease. If depression and sadness get in the way of daily activity, seek help—for your mind and your body. Support is available and you need not be alone.
9. Internalizing emotions.
A study reported by the National Institutes of Health found that:
“…excessive use of denial and suppression/repression has important psychophysiologic effects linked to tumor biology and host-defense. Recent studies reveal that psychosocial stressors which are met by inadequate and repressive coping styles are associated with changes in immunocompetence, including both humoral and cell-mediated immunity.”
Let it out! In a constructive way, of course. Talk to a friend or counselor, journal, walk in the woods and talk to the trees—whatever feels most comfortable to you to vent your feelings. Once identified, not only will you feel better but you will be better able to manage stress and handle the issues that arise, allowing your mind and body to heal.
10. The Letdown Effect.
All too often, we get sick while on vacation. While it seems ridiculously unfair, there’s a physiological reason: what has come to be called the “letdown effect”. After periods of stress, there is a sudden change in hormone levels affecting the immune system and the body becomes more susceptible to illness. Try some activities to ease your system back to normal hormone levels like word games, moderate exercise, or chess.
11. Not enough nutrients.
The immune system relies on certain necessary vitamins and minerals to optimally perform. Simple deficiencies in vitamins A, B6, B9 (folic acid), C, D, and E, or copper, iron, selenium, and zinc can contribute to decreased immune function. Do your research to make sure you get the right amount of nutrition through your food. Consult a healthcare provider before taking any supplements and remember that whole-food sources are better than synthetics.
Chronic immune deficiency will hurt you. Take care of yourself.