Many studies have shown that latex films form an excellent barrier to pathogens and a vastly superior one to vinyl films and to most other competitive materials. This is largely due to the excellent film-forming nature of natural rubber latex. Natural rubber films are very strong and are closely fitting (tactile performance is not impaired and may even be enhanced). In the case of gloves they both protect the object being handled (in the case of medical gloves this is the patient, but this may also be other objects: drugs, foodstuffs, electronic components, etc), and the wearer.

It must be noted that ordinary natural rubber latex gloves will not be appropriate for handling fuels, most solvents and certain chemicals: most large suppliers of industrial gloves will provide appropriate guidance for the correct protection for handling dangerous chemicals.

Many studies have shown that natural rubber latex films form an excellent barrier to the transmission of the AIDS virus. This includes evidence from persons who have had routine latex-condom-protected sexual intercourse with AIDS-infected partners, and who have remained free from infection.

Natural rubber latex is also used in catheters, balloons, some medical tubing, elastic thread, and some adhesives, but its primary market is in gloves which are predominantly consumed by the medical sector, notably within the United States. The size of the US market is more than 25 billion units (that is all dipped gloves). The European market is smaller. Condoms may be widely used, but in tonnage terms the market is far smaller than that for gloves.

About 10 per cent of latex extracted from the rubber tree, Hevea brasiliensis, is manufactured into latex products. That is, the latex is consumed after it has been concentrated by centrifuging (which removes some of the water and much of the proteinaceous material) and has been preserved with ammonia. A limited quantity of latex concentrate is also produced by creaming which it is believed reduces the amount of proteinaceous material and some is subjected to additional centrifuging for the same reason.

Gloves and condoms are produced by dipping, whereby a former (made of porcelain, glass, etc) is dipped into a tank of latex. Most gloves are produced from prevulcanized latex (latex concentrate mixed with sulphur and accelerators), but some are produced from "straight latex" where the process includes an extra dipping operation. Following the formers being dipped into the tank of latex, the coated former is dipped into a coagulant (typically calcium nitrate) to gel the latex. The coated formers are then heated in a continuous oven which dries and vulcanizes the latex films.

The gloves or condoms are then stripped from the formers, leached (by washing to remove accelerator residues and proteins), inspected and packed. The process is normally continuous and performed on a long line. In some cases the gloves may be subjected to additional processes such as chlorination prior to inspection and packing. Inspection is a labour-intensive process.

The principal glove producing countries are Malaysia, Thailand, China, India and the USA.

The remaining 90 per cent of latex (over 5 million tonnes) is converted into dry rubber either by the deliberate coagulation of the latex, or by processing the naturally coagulated material which forms in the tapping cup, or by reprocessing smallholder rubber which has been coagulated prior to sale. These precoagulated materials are subjected to milling and washing to remove any material which may have contaminated the rubber during collection and transportation. A relatively small amount of dry rubber is produced by producing sheets which are dried by solar heating: this is an especially environmentally form of natural rubber. Most natural rubber is dried by using a limited amount of fossil fuel.

In general terms, dry natural rubber requires the use of about a tenth of the fossil fuel required to produce synthetic rubbers. Furthermore, the rubber tree is capable of reabsorbing the carbon dioxide generated by burning discarded rubber products, such as gloves and tyres.

The bulk (over 70 per cent in the USA) of dry natural rubber is used in tyres, especially those which call for high performance, notably aircraft and truck tyres. It is the ability of natural rubber to be able to dissipate the heat generated by the use of such tyres which contributes so much to air and road safety. Without natural rubber there would be more air and road accidents: tyres based on 100 per cent synthetic rubber would not be as safe.

There have been some suggestions that latex proteins can survive the heat employed to dry the bulk of natural rubber, the heat involved in vulcanizing the tyres and the great heat generated at the tyre/road or runway interface to be liberated into the atmosphere. These must be remarkable proteins. On a similar basis one might expect the deadly gas, phosgene, used in the manufacture of polyurethane raw materials to survive in car seating and in a wide range of clothing, or the highly carcinogenic benzene used in the preparation of synthetic elastomers to be associated with car tyres (which are mainly based on synthetic rubber).

It should be noted that highly carcinogenic dioxins are produced during the combustion of vinyl gloves: medical products must be incinerated after use. Any substitution of latex by vinyl will increase the risk of dioxin releases into the atmosphere. Many synthetic elastomers contain at least trace amounts of major carcinogens.

Esah Yip, Kristiina Turjanmaa and Soili Makinen-Kiljunen conclude that, as tested by the best methods available, dry rubbers and dry rubber products (cut thread, hot water bottles and divers' flippers were tested) have not only extremely low residual extractable protein contents, but also very low or negligible allergenicity. This is not withstanding the fact that there are relatively fewer dry rubber products used in the healthcare sector where prevalence of Type 1 hypersensitivity has been reported. Furthermore, products such as the cut threads which are often used as medical bandages, are not likely to pose any problem since they are generally covered by fabric thereby minimising any contact with the human skin. Therefore NR dry rubbers and dry rubber products are essentially not affected by the protein allergy.

There are many references to airborne latex particles as distinct from airborne cornstarch particles incorporating latex protein. Without the cornstarch or other powdery carrier the probability of airborne latex is extremely low as latex film is a naturally coherent material. This is the reason for the excellent barrier properties and why natural rubber is used in high performance tyres (and why it is not simple to dismantle and recycle tyres). It is also the reason why it is relatively difficult to produce latex concentrate: left on its own the material will cohere to itself as anyone who has used latex adhesives will be well aware the adhesive tends to form long "strings".

It is possible to produce gloves with greatly reduced protein levels and it is also possible to produce powder-free latex gloves. Many of the early cases of latex protein allergy were due to exposure to gloves containing extremely high levels of protein. These were gloves which had been produced under poor factory practice: where the dipping plant had not be cleaned to remove proteinaceous deposits or where the gloves had been leached for too short a time, or where inadequately centrifuged latex had been used as the raw material. Producers were tempted to cut corners to meet demand and to supply a cheaper product to meet the supposed wishes of the market for a low cost commodity.

Members of the Malaysian Rubber Glove Manufacturers' Association intend to phase out the production of powdered gloves in favour of powder-free gloves. A survey amongst the Association's members showed that two-thirds of them could convert to low-protein, powder-free gloves within a year. The Standard Malaysian Glove is being introduced in an endeavour to manufacture gloves to defined limits for protein content.

Natural rubber is produced by an environmentally friendly industry and assists in diminishing the environmental damage caused by the widespread use of fossil energy sources. It tends to be produced by poor farmers in tropical countries who tend not to receive low incomes in relation to the large amount of work expended.

It is probable that at least 20 million people are reliant upon natural rubber cultivation for their primary source of income. Contrary to some myths being circulated in the United States the producers of natural rubber do not suffer from skin problems due to contact with the material.

References which show the poor relative performance of vinyl films

Hirshfeld, J.W. Bacterial contamination of wounds, from the air, from the skin of the operator and from the skin of the patient. Surgery Gynecology and Obstetrics, 1941, 73, 72.

Klein, R.C., Party, E. and Gershey E.L., Virus penetration of examination gloves. Biotechniques, 1990, 9 (2),196-9

Korniewicz, D.M. et al. Leakage of virus through used vinyl and latex examination gloves. Journal of Clinical Microbiology, 1990, 28, 787.

Korniewicz, D.M. et al. Leakage of latex and vinyl exam gloves in high and low risk clinical settings. American Industrial Hygiene Association Journal, 1993, 54, 22.

References to of natural rubber's effectiveness as a barrier to AIDS

Daigleish, A.G. and Malkovsky, M. Surgical gloves as a mechanical barrier against human immunodeficiency viruses. British Journal of Surgery, 1988, 75, 171.

Fiehn, N.E. and Westergaard, 3. Physical and microbiological quality of five different examination and surgical gloves before and after use in dental practice. Zentralblatt fur Hygiene und Umweltmedizin, 1993, 195, 27.

Gruninger, S.E., et al. Human immunodeficiency virus type I infection among dentists. Journal - American Dental Association, 1992, 123, 57.

Mead, P.B. AIDS: risk to the health profession. Clinical Obstetrics and Gynecology, 1989, 32, 485.

Molinari, J.A. HIV, health care workers and patients. Journal - American Dental Association, 1993, 124, 51.

Schiff, S.J. A surgeon's risk of AIDS. Journal of Neurosurgery, 1990, 73, 651.