The latex rubber condom produced today is more reliable than ever before, due primarily to improved quality management, but also to better formulations and packaging. It is also generally safer in terms of possible health problems, although some new concerns are arising regarding allergic or other toxic reactions to various components of latex condoms such as vulcanization accelerators, latex proteins, spermicides and finishing powders.
Latex Formulation
Latex condoms are made by mixing various chemicals with natural liquid latex, a process that affects the chemical and mechanical properties of the final product. Natural latex rubber deteriorates due to exposure to oxygen, ozone, heat, humidity, ultraviolet and visible light, mechanical fatigue or heavy metal contamination. Recent formulation improvements have focused on the chemical processes of oxidation and vulcanization and on the mechanical properties of stress and strain.
Oxidation is the deterioration of latex due to exposure to oxygen. To help prevent oxidation, most manufacturers now add antioxidants to the latex formulation, usually phenol compounds.
Vulcanization, a chemical curing process, increases the strength and resilience of rubber by forming sulfur-sulfur crosslinks between polymeric strands of the latex. Unvulcanized latex rubber is weak, loses its shape and can be sticky like chewing gum. Vulcanization enables elastomeric materials to return to their shape more easily after being stretched and reduces the amount of change in shape. The degree of vulcanization is controlled by the quantity and type of vulcanizate and temperature. Vulcanizing agents can act too fast or not fast enough, too thoroughly or not completely enough. If chemical agents added to the formulation work too long, excessive vulcanization in the package occurs, which can make condoms brittle, stiff and less elastic when opened and used.
In recent years, manufacturers have improved the control of the vulcanization process, using chemical activators and accelerators in a more reliable process. This has resulted in minimal or no in-package vulcanization.
Changes in the formulation affect the mechanical properties of stress and strain. A force can be applied to compress or to stretch a material. With condoms, stress refers to the amount of force needed to extend the latex rubber a specified amount; stress is related to condom strength. Strain refers to how far latex rubber can be stretched and is related to elasticity. Both stress and strain contribute to the resistance of latex to breakage.
The relationship of stress and strain properties is called "modulus." Researchers working with condoms generally use the concept of "Young's modulus," which refers to a ratio of stress over strain (with stress as the numerator and strain as the denominator). Manufacturers, on the other hand, use the concept of "percent elongation modulus." This refers to the amount of stress per unit of cross-sectional area of the condom, measured in megapascals of pressure, at a given extent of strain through elongation, usually at 300 percent or 500 percent.
In either case, the term modulus refers to the stiffness or hardness of a material: a low-modulus material is more pliable and elastic, such as rubber bands, and a high-modulus material is stiffer but able to withstand a greater force, such as steel. This monograph uses the concept of "Young's modulus," since the studies discussed here use that concept.
Since latex condoms need to be both elastic and strong, the combination of the mechanical properties determines how reliably a condom performs. Manufacturers appear to be moving toward producing a more elastic condom. Findings from a series of FHI studies at six international sites compared a higher-modulus condom, called "extra-strong," with a lower-modulus, more elastic condom in human use. More than 3,000 of each type of condom were used. The more elastic condom broke less frequently (3.3 percent), compared to the "extra-strong" condom (4.3 percent), although the difference was not statistically significant. (Abeywickrema; Alvarado; Cordero; Figueroa; Ndumbu; Sidibe)
The mechanical properties of latex rubber condoms can change during aging if the latex film is not well formulated and protected from oxidation. Findings from a study conducted by PATH, with support from the FDA and FHI, found that stress and strain properties of latex condoms appear to deteriorate for different reasons, some oxygen-dependent and some oxygen-independent. Stress properties appear to be very susceptible to deterioration due to oxidation, while strain properties appear to be more sensitive to deterioration due to excessive vulcanization. The study compared changes in condoms artificially aged in the laboratory to those stored for various lengths of time and under various conditions in the United States and in four other countries. (Free)
By evaluating the stress and strain properties of new and aged condoms from the same condom batch, laboratory tests can yield a "fingerprint," revealing one of three predominant causes of deterioration of the condom:
- Oxidative Deterioration -- A decrease in stress properties, with little or no decrease in strain properties, suggests oxygen-permeable or defective packaging (i.e., a hole in the package or an insufficiently sealed condom package) and a lack of antioxidant protection in the latex formulation.
- Shelf Vulcanization -- A decrease in strain properties, with little or no decrease in stress properties, suggests that the condoms were well protected from oxidative deterioration by good packaging but underwent shelf vulcanization, resulting in a stiffer, less elastic condom.
- Localized Deterioration -- A decrease in one indicator of stress properties (air burst pressure), with little or no decrease in the other two stress indicators (tensile strength and break force), suggests localized deterioration at the tip or parts of the condom unprotected by the condom roll. It also suggests high-temperature exposure and/or poor packaging. (Free)
Condom Packaging
Currently, most latex condoms are packaged in plastic cellophane, aluminum foil, or aluminum foil laminated with plastic cellophane. Some paper and paper laminates have been used worldwide, and may still be used in developing countries. The type of packaging affects the extent of condom deterioration during storage due to ultraviolet or visible light, oxygen, ozone, humidity, friction in the package and extreme temperatures.
For at least a decade, experts have known that translucent packages were generally not as protective as opaque packages. Research showed that condoms stored in translucent packages and exposed to ultraviolet (UV) light may deteriorate in only a matter of hours, while opaque packages protected condoms from UV exposure. (Anonymous 1987)
A recent study of package integrity conducted by PATH and supported by USAID and FHI showed convincingly that foil packaging offered the most protection from oxidative deterioration. The study found that plastic packaging is permeable to oxygen, while foil packaging is not. The study compared condoms stored for 36 to 48 months in a natural, tropical climate with those in a more temperate, climate-controlled setting. The condoms were tested yearly for strength, package integrity and oxygen content. Condoms from two U.S. manufacturers were used. (PATH)
The condoms packaged in only plastic cellophane deteriorated much faster than did those packaged in plastic-foil laminates. The decline in air burst pressure and volume from the air burst test were significantly higher for cellophane-packaged condoms, indicating the occurrence of oxidative deterioration in those condoms (p< 0.0012). This suggests that cellophane packaging is permeable to oxygen and thus may not prevent oxidative deterioration of condoms from occurring. A gas analysis of the two types of packaging found that oxygen content was consistently higher in the cellophane packages. (PATH)
A study focusing on the shelf life of condoms, conducted by PATH in conjunction with the FDA and FHI, found that condoms stored in impermeable, sealed foil packages have a shelf life beyond five years, even under tropical conditions. The study found that unpackaged condoms stored at high temperatures showed sharp decreases in air burst properties (both volume and pressure), rendering the condoms unfit for use within a three- to six-month period. (Free)
Currently, most studies by manufacturers of latex condoms that are naturally aged indicate that the shelf life of these condoms can be as long as five years, as long as they are not lubricated with spermicides. Spermicides have a shelf life of two to three years, however, thus shortening the shelf life of spermicidally-lubricated latex condoms.
Following a recent FDA ruling, condom manufacturers in the U.S. will be required to support their shelf life labels with laboratory test data. Beginning in March 1998, the labeling of latex condoms produced in the U.S. must contain an expiration date based upon the results of physical and mechanical testing performed after exposing naturally-aged and accelerated-aged condoms to varying conditions.
Latex Allergies
Research in recent years has raised concern about sensitivity and allergic reactions to latex condoms due to proteins in natural latex, to chemicals added to latex formulations, and to spermicides added to lubricants at the factory. Latex allergies are quite rare among the general population, however. Concerns about latex allergies should not inhibit sexually active people who are at risk of exposure to STDs from using condoms, since the risks associated with unprotected sexual contact are far greater than those from exposure to latex.
Some proteins found in natural rubber latex can cause sensitivity or allergic reactions. Condom manufacturers remove many of these natural proteins using a washing process called leaching. Leaching is done by dipping the condom in a series of baths, which usually contain hot water or a hot caustic solution. Leaching not only removes latex proteins, but may remove other components of latex as well.
The release of latex proteins can also result from interactions between the latex device and other chemicals, including the accelerators, antioxidants and dyes added to the latex formulation. (Rademaker; Turjanmaa) Accelerators, which increase latex cross-linking during vulcanization, can also cause allergic reactions.
Sensitivities or allergies usually develop gradually when mucosal and/or peritoneal surfaces come into repeated contact with protein allergens released from natural rubber latex. (Stratton; Deusch) The vagina and opening of the penis are both mucosal surfaces.
No studies have found that latex condoms result in high allergy rates. Among those allergies due to latex condom exposure, none has been extremely serious. Most allergic reactions to latex are minor, such as redness, itching, swollen and watering eyes, and swelling or inflammation, which subside when latex exposure is withdrawn. (Tomazic; Sussman) Persons allergic to latex should consider using synthetic condoms if they are available.
Experts are concerned that allergies to latex condoms may be increasing in prevalence and severity. Latex allergies are already a serious and growing problem among certain populations, due to the increased use of latex examination gloves and catheters.
In 1993, as a result of increased latex sensitivities and allergies among its patients, a hospital in Springfield, MA, USA, stopped using any latex medical products, using synthetic products instead. Recently, several manufacturers have received FDA clearance for "low-protein" surgical/examination gloves which are made by including additional and more complex leaching processes. In 1997, the FDA ordered makers of all medical devices that contain natural rubber latex, which include condoms, to warn that the products may cause allergic reactions. The order also covered packaging of the devices.
The presence of nonoxynol-9 (N-9) in the lubricant of condoms may increase the amount of protein released from the latex. A recent study found that protein levels from latex condoms with N-9 in their lubricants were approximately five times higher that the protein levels from condoms without N-9 in their lubricants. (Stratton) By increasing the amount of protein released from latex, N-9 may actually trigger a latex protein reaction.
Some condom users may be sensitive or allergic to N-9 itself. (Fisher; Dooms-Goosens) These users must be sure to use only condoms that are not lubricated with spermicides. In the U.S. about one-third of the condoms lubricated at the factory contain spermicides, usually in the form of N-9.
Dry Powders
Concerns have also emerged about the possible toxic effects of talc and other substances used in the finishing process of the condom. Dry dusting powders help keep the rolled up latex condom from sticking to itself. To accomplish this, manufacturers have used cornstarch, talc, mica, calcium carbonate, silicon dioxide, magnesium carbonate, lycopodium, dry silicone and other powders, with cornstarch currently the most commonly used. (Kang)
Talc, a natural mineral magnesium silicate, is a good dry lubricant. When used for cosmetic purposes, talc has not been a problem. (Wehner 1994, 1996) However, some experts think that when talc comes into contact with mucosal surfaces, it may be toxic. Because surgery usually involves contact with open or mucosal tissues and concerns were raised about the possible toxic effects of talc as a result of talc-coated surgical gloves, the use of talc on surgical gloves was stopped several years ago. (Kasper) When talc is used as a finishing powder on latex condoms, female partners of condom users may face a health risk due to the talc on the surface of latex condoms. The talc could migrate up the vagina, a mucosal surface, into the upper female reproductive tract, which may result in fallopian tube fibrosis with subsequent infertility. (Wehner 1996)
For many years, talc was the preferred dusting powder and was once commonly used in latex condoms manufacturing. The relevance of using talc on condoms seems to fall somewhere between the realms of surgery and cosmetic use, but enough concern has emerged to cause a shift away from using talc in condom manufacturing. Currently, while condom manufacturers report that they do not use talc, (Anonymous 1995) some appear to have continued using it.
Cornstarch has become the new industry standard for finishing. While not as problematic as talc, it too could pose problems. Cornstarch is a heavily cross-linked carbohydrate with particle sizes ranging from 1 to 3 microns in diameter. A recent study found that, when used with surgical/examination gloves, cornstarch binds to allergenic latex proteins, and the more cornstarch used, the more protein binding occurs. (Tomazic) The latex-protein contaminated cornstarch particles are small enough to become airborne and can expose any persons in the vicinity to the latex proteins via the lungs, mouth, nose, eyes and skin. Direct contact with latex is not necessary to initiate a reaction.
Any wet lubricant applied to condoms before packaging should decrease the amount of airborne cornstarch. However, the cornstarch/latex protein complexes are more easily shed than latex proteins bound to the condom and could result in sensitivity or allergic reactions. Also, the airborne cornstarch/latex protein complexes remain an issue with unlubricated condoms.
Further research needs to be done to determine whether the dry powders currently used produce detrimental effects on users due to mucosal exposure. Researchers need to find new dry finishing powders, with one possibility being silicone powder. It has been widely used in other industries.
Conclusion
In recent years, better quality management, new research and the actions of manufacturers have led to a more reliable and safer latex condom.
Manufacturers now produce condoms that are more elastic with a chemical formulation that includes more antioxidants and better-controlled vulcanizates -- all steps that ensure condoms do not deteriorate as readily as in previous years. To better protect latex condoms from deterioration, manufacturers are using more impermeable, foil packaging; switching from plastic to foil or foil laminate packaging; and focusing more attention on tight package seals. These steps help preserve the integrity of the condoms, even under the most adverse storage conditions.
On the health front, manufacturers have moved away from using talc as a finishing powder, due to concerns about its possible toxicity. More research is needed on the safety of using cornstarch, the current preferred powder for finishing, or on determining a safer finishing powder. New research on allergies to latex proteins has also focused more attention on better leaching of proteins from the natural latex. Manufacturers are now able to produce condoms with less latex protein. More research is also needed to determine whether adding spermicides to the lubricant at the factory could result in more allergic reactions to latex.
by Caroline E. Gilmore
References
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- Anonymous. Monitoring condom quality. Outlook 1987;5(3):2-5.
- Anonymous. Why is talc considered a problem substance? Contracept Tech Update 1995;16(11):136.
- Cordero M, Piedrahita C, Holschneider S, et al. Analysis of Actual Use Breakage Rates of Standard and Extra-strong Condoms: Dominican Republic. Durham, NC: Family Health International, 1991.
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- Ndumbu F, Steiner M, Piedrahita C, et al. Analysis of Actual Use Breakage Rates of Standard and Extra-strong Condoms: Kenya. Durham, NC: Family Health International, 1991.
- PATH. Final Report - Package Integrity Study. Seattle, WA: Program for Appropriate Technology in Health, 1996.
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- Sidibe M, Steiner M, Joanis C, et al. Analysis of Actual Use Breakage Rates of Standard and Extra-strong Condoms: Mali. Durham, NC: Family Health International, 1991.
- Stratton, P. Nonoxynol-9 lubricated latex condoms may increase release of natural rubber latex protein. Presentation at the International Conference on AIDS, Vancouver, BC, Canada. July 1996.
- Sussman G, Beezhold D. Allergy to latex rubber. Ann Intern Med 1995;122:43-46.
- Tomazic V, Shampaine E, Lamanna A, et al. Cornstarch powder on latex products is an allergen carrier. J Allergy Clin Immunol 1994;93:751-58.
- Turjanmaa K, Reunala T. Condoms as a source of latex allergen and cause of contact urticaria. Contact Dermatitis 1989;20:360-64.
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- Wehner A, et al. Biological effects of cosmetic talc. Food Chem Toxicol 1994; 32:173-84.
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