There are many environmental factors and contaminants that can cause allergies and sensitivities as well. This puts considerable strain on your immune system. The allergic reaction is continuous, which keeps your immune system in a constant state of attack. Ultimately, it weakens your immune system making you more susceptible to disease.
Lyme patients often experience hypersensitivity to environmental allergies. This is usually due to the high amount of toxic load in the body. If toxins and allergens are not removed from the environment, it can lead to auto-immune diseases.
If you suspect there are allergens and contaminants in your home you can always hire someone to do an air quality analysis. This can often narrow down the potential harmful contaminants and gives you a focus on what to change or remove. Some environmental contaminants (like lead or asbestos) can cause considerable harm to the human body and need to be removed immediately and properly. Have an expert inspect your home for these types of hazards.
Home Building Products
The products used to build a home can release toxins into the air. Carpeting and laminate flooring has plastic derivatives that can slowly release toxins into the air. Polyurethane coatings on wood can do the same thing. If you are replacing flooring in your home, do your research before choosing a product. Countertops and cabinets can also contaminate the air. Know the risks and assess what the best option is. Cheaper is not necessarily better.
Mold
Maintaining your home to prevent mold and other harmful deteriorating effects is important. Mold contamination can cause all sorts of serious ailments.
If there has been a leak that did not dry quickly, mold could be growing inside your ceilings or walls. If your basement or bathroom is damp, mold can grow. Ventilation and regular cleaning is also crucial.
If there is flooding or leaking, it is important to have the water cleaned up and the room dried properly to prevent mold growth. Maintaining the roof, siding, windows, and doors on a house are the best prevention for mold.
Radon
Radon exposure is a serious issue and is in approximately 1 in 3 homes. It is estimated to cause 20,000 deaths due to lung cancer each year in the U.S. alone. Before you buy a house, have this tested. If you are unsure in your own home, have it tested.
Radon is a radioactive gas with no color, odor, or taste. It is sometimes found in groundwater, soil, confined spaces, or building products. In many cases this can be an issue in the workplace.
Lead
There may be lead paint if it is an old home inside or out. If this is the case, particularly if the paint is deteriorating and chipping, it will need to be removed by a licensed specialist in lead removal. Lead is also sometimes found in drinking water form deteriorating pipes. Lead is highly toxic to animals and humans, particularly children when inhaled or ingested(See the Heavy Metals & Parasites page).
Asbestos
Asbestos can be found in insulation in older homes. It was also used to cover ductwork, pipes, and some old knob & tube wiring. It can also be found in old electrical cords and fireproofing materials. This was widely used in industry as a fire retardant and insulator up until it was banned in 1989.
Asbestos fibers stick to the tissues of the lungs. Over time it creates scar tissue and eventually can cause Cancer. When in doubt, have an expert inspect and remove it if necessary.
Ventilation System
Having an adequate ventilation and filtration system can reduce air borne allergens significantly. There are many options available and it is a very personal choice. Do your research and have an expert assess your home.
Air movement is essential. Change filters often. In some cases, you may need to replace or reseal windows and doors and avoid leaving them open.
Pet Allergies
Pet Allergies are common amongst most people. Generally it is an allergy to the dander, not the hair of the pet. Some people are allergic to cat saliva as well. Using hypoallergenic bedding and washing it regularly can help. Hardwood or tile floors instead of carpet are easier to keep allergen free. Keep pets brushed and bathed. Use filtration in your ventilation system and change filters often to limit exposure. If allergies are severe, you may need to relinquish having a pet.
Dust
Dust in the air causes allergic reactions in a lot of people worldwide. Dust contains tiny bits and particles of the fabrics, dirt, and items in the environment. It also contains tiny microscopic organisms called dust mites. They feed on dead flakes of skin and turn it into dirt. The waste products of these creatures invoke an immune response in people who have an allergy to it. It often causes asthma and many other allergic problems. Keeping floors and furniture clean and using filtrations systems can minimize exposure to this.
Work Environment
Many people work in environments where they are subjected to contaminants and irritants. If you have allergies or sensitivities to these, you may have to change your location of employment. In some cases, this may seem impossible. But, if there is any way to limit your exposure, the healthier you will be and the better quality of life you will lead.
Some of these things can include exposure to lead, asbestos or mold in old buildings, fumes, manufacturing products, chemicals and products used at the work place, environmental contaminants in fields such as construction, medical waste, etc.

Environmental factors can quickly diminish immune function.