You could be 30 or 40 years old and still not show symptoms of asthma. Yet gradually your lungs are changing, and the cause is related to your work.  Now you have asthma, and all symptoms that go with it.

What I'm describing here is one of the more recently defined types of asthma called Occupational Asthma.

The theory here is that, according to the Mayo Clinic, if you have the asthma/ allergy gene, and you are exposed to certain irritants and allergens in the workplace, over time, these certain irritants may actually irritate the air passages of your lungs and make them more sensitive to these allergens.

The Mayo Clinic also notes that constant exposure to certain allergens can cause your body to develop a sensitivity (allergy) to it.  Your body identifies the substance as a "threat" and later exposed will cause your body to attack it.  During the attack your body releases chemicals like histamine, which cause inflammation of the lungs. 

According to the Mayo Clinic, long-term exposure to any of the following may increase your risk of getting asthma: 

• Animal substances, such as proteins found in dander, hair, scales, fur, saliva and body wastes.
• Chemicals, such as anhydrides, diisocyanates and acids used to make paints, varnishes, adhesives, laminates and soldering resin. Other examples include chemicals used to make insulation, packaging materials, and foam mattresses and upholstery.
• Enzymes used in detergents, flour conditioners, some pharmaceuticals and meat tenderizers.
• Metals, particularly platinum, chromium and nickel sulfate.
• Plant substances, including proteins found in natural rubber latex, flour, cereals, cotton, flax, hemp, rye, wheat and papain, a digestive enzyme derived from papaya.
• Respiratory irritants, such as chlorine gas, sulfur dioxide and smoke.
• 2nd hand smoke: Click here to learn how your co-workers cigarette smoke can cause asthma.
• Strong smells: Heavily scented cologne and perfume
• High or low humidity: Click here to learn these are both linked to asthma
• Hot or cold air: Extremes in weather can trigger or cause asthma as you can read here.
• Physical exertion: Click here to learn why some athletes are at increased risk for developing exercise induced bronchospasm.

According to the American Accedemy of Allergy, Asthma and Immunology (AAAAI.org) as many as 15 percent of asthmatics in the U.S. have occupational asthma.

Bakers commonly develop allergic asthma from breathing in flower and cereal grains.  About 5 percent of those working with lab animals or latex gloves develop allergic asthma. Another 10 percent are those exposed to chemicals from spray painting, insulation, rubber and foam. 

Others at high risk include (according to Mayo clinic):  janitors and hair dressers due to sprays, healthcare workers due to latex exposure (although many hospitals now use non-latex products), adhesive handlers (chemicals), pharmacists (drugs and enzymes), carpenters (wood dust), solderers (metals), and textile workers (dyes).