The chemistry of latex
Latex products are manufactured from a milky fluid derived from the rubber tree, Hevea brasiliensis, which is indigenous to Brazil. Natural rubber latex consists of a complex mixture of polyisoprene, lipids, and phospholipids. In addition, proteins and chemicals such as sulfur, ammonia, mercaptobenzothiazole, thiuram, and antioxidants are added to this fluid during the processing and manufacture of commercial latex.
The protein molecules in latex are responsible for the majority of generalized allergic reactions to latex, which can range from mild to severe. There are at least 240 potentially allergenic proteins in the processed latex product. "One of the proteins in latex that is known to cause allergy is hevein. There are about 14 others that have been identified and more than 200 that have not," according to Dr. Beezhold, Senior Scientist and Director of the Laboratory of Immunobiology at the Guthrie Research Institute, Sayre, Pa.
What happens during a latex allergy reaction
A latex reaction occurs when the body treats latex proteins as it would more harmful foreign substances. To destroy potentially bacteria and viruses, the body creates proteins, called antibodies or immunoglobulins, which are targeted against these invaders, which are called antigens. The antibodies help destroy the antigen by attaching to its surface, which makes it easier for other immune cells to destroy it.
In latex-sensitive individuals, the body develops special antibodies against the latex proteins. These special antibodies, called immunoglobulin E or IgE, cause the symptoms of an allergic reaction. "Scientists theorize that IgE was at one time our bodies' line of defense against parasitic infections," says Dr. Beezhold. "Now there are not many parasites in our modern environment, and the IgE seems to have turned on allergens."
Some people, categorized as atopic, are more prone to allergies because they produce IgE in large quantities. During the sensitization period, this surplus of IgE coats specialized immune cells called mast cells, which are located in the skin. "Mast cells contain a chemical called histamine. When the allergen contacts the IgE proteins on the mast cells, these cells explode, releasing the histamine, which causes the symptoms of allergy, including watery eyes, sneezing, itching, and in some cases, more severe reactions," says Kevin Kelly, MD, Professor at the Medical College of Wisconsin, Milwaukee. Under normal circumstances, if the allergen were truly harmful, these symptoms would help the body rid itself of these invaders. In this case, however, the reaction, not the allergen, causes the most harm.
The latex proteins find their way into a person's system either by being absorbed through the skin or through mucous membranes. The proteins have been shown to fasten to powder that is used on some latex gloves. When powdered gloves are worn, more latex protein reaches the skin. Also, when gloves are changed, latex proteins that are fastened to the powder particles get into the air, where they can be inhaled and contact body membranes. According to Dr. Kelly, "Even if you use latex-free products for a case, a highly sensitized person can react to the powder-bonded latex proteins that are still present from the case before."
"With latex allergy, there is a threshold of exposure; you can only be exposed to so much latex before you cross over that line," advises Dr. Kelly. "With the advent of standardized precautions in healthcare facilities, our exposure to latex increased over a hundred fold, and we crossed over that threshold. We saw many workers developing latex allergy." But there were still many who didn't.
Predicting who will develop an allergy and when isn't an exact science. It's clear that atopic people are genetically disposed to overproduce IgE. Individuals who are allergic to certain foods, including avocado, banana, chestnuts, kiwi, and papaya, are also at greater risk. "Because these foods contain a protein that is very similar to hevein, they are known to cross-react," notes Dr. Beezhold. "Patients with latex allergy will sometimes develop these food allergies, and in some cases it can go the other way, where people with the food allergy can develop a latex allergy."
An individual could be atopic and not develop an allergy for years, or he or she may develop it right away. According to Dr. Kelly, this is because all individuals have their own unique biological variables and their own threshold for exposure. Researchers agree, however, that more exposure increases the chances that an individual will eventually have a reaction to latex.
Types of latex reactions
Reactions to latex products include irritant contact dermatitis, allergic contact dermatitis, and Type I IgE allergic reactions. Only the last constitutes a latex allergy. Contact dermatitis, both irritant and allergic, is the most common reaction associated with latex and its additives.
Irritant Contact Dermatitis: The most common reaction to latex products is irritant contact dermatitis-the development of dry, itchy, irritated areas on the skin, usually the hands. This reaction is caused by skin irritation from using gloves and possibly by exposure to other workplace products and chemicals. The reaction can also result from repeated hand washing and drying, incomplete hand drying, use of cleaners and sanitizers, and exposure to powders added to the gloves. Irritant contact dermatitis is not considered to be a true allergy.
Allergic Contact Dermatitis: Allergic contact dermatitis (also called delayed hypersensitivity and sometimes called chemical sensitivity dermatitis) results from exposure to chemicals added to latex during harvesting, processing, or manufacturing. These chemicals can cause skin reactions similar to those caused by poison ivy. As with poison ivy, the rash usually begins 24 to 48 hours after contact and may progress to oozing skin blisters or spread away from the area of skin touched by the latex. Says Lise Borel, DMD, National Director of the National Latex Allergy Network, "People who experience allergic contact dermatitis and continue to use latex products put themselves at an increased risk for developing a latex allergy, because the cracked, itchy skin gives the latex proteins easy access into the body."
Latex Allergy: Latex allergy (sometimes called immediate hypersensitivity) can be a more serious reaction to latex than irritant contact dermatitis or allergic contact dermatitis. Although the specific allergen and the amount of exposure needed to cause a reaction is not known, exposures at even very low levels can trigger allergic reactions in some sensitized individuals.
Allergic reactions usually begin within minutes of exposure to latex, but they can occur hours later and can produce various symptoms. Mild reactions to latex involve skin redness, hives, or itching. More severe reactions may involve respiratory symptoms such as runny nose, sneezing, itchy eyes, scratchy throat, and asthma. In rare cases, shock may occur, but a life-threatening reaction is seldom the first sign of latex allergy.
Diagnosing latex allergy
The methods that are currently used to detect a latex allergy do not always provide consistent identification of what antigens are causing the reaction-studies suggest that the culprit could be any one of a number of latex proteins. Latex allergy should be suspected in anyone who develops certain symptoms after latex exposure, including nasal, eye, or sinus irritation; hives; shortness of breath; coughing; wheezing; or unexplained shock. A physician should evaluate any exposed worker who experiences these symptoms, since further exposure could result in a serious allergic reaction.
Allergists can diagnose latex allergy using the results of a medical history, physical examination, and testing. There are three tests that are currently used to diagnose a latex allergy.
IgE Serum Blood Test: Blood tests cleared by the Food and Drug Administration are available to detect latex antibodies.
Skin Test: Skin tests involve scratching or pricking the skin through a drop of liquid containing latex proteins. Itching, swelling or redness at the test site shows a positive reaction. However, FDA-approved materials are not yet available to use in skin testing for latex allergy. This test should only be performed at medical centers with staff who are experienced and equipped to handle severe reactions.
Challenge Test: During the challenge test, the person puts on a finger from a latex glove, and it is removed after 30 minutes. Like the skin test, the challenge test should only be done at medical centers that can handle a severe reaction.
A patch test is also available to diagnose allergic contact dermatitis. In this FDA-approved test, a special patch containing latex additives is applied to the skin and checked over several days. A positive reaction would include itching, redness, swelling, or blistering where the patch covered the skin.
The best means of treatment is prevention. Experts recommend using low-protein, powder-free gloves to prevent sensitization. "I am confident manufactures can produce a good barrier with low-protein latex," says Dr. Beezhold. "And now that sixty to seventy percent of healthcare facilities are now using low-protein gloves, we've seen signs that the incidence of latex allergy cases is declining."