When NR allergenic proteins first enter the body of a sensitive individual, IgE which recognises allergen epitopes (binding sites of antibody) is produced and circulated around the body through lymph nodes and blood without any allergy symptoms. However, when allergen with the same epitopes enters the body again at a later time, it binds to the IgE on the cell surface, causing the cells to release pre-formed mediators, which causes symptoms of allergic inflammation such as heat, pain, swelling, redness, asthma, itchiness and in some rare cases anaphylaxis. These allergic reactions can occur within 5 - 30min. These reactions could also be elicited in NR protein sensitive individuals if they ingest allergens with similar epitopes, such as in the case of avocado, banana, chestnut and kiwi fruit among many others. This phenomenon is known as latex-food cross reactivity. However, it is important to note that not all food-allergic individuals are sensitive to NR proteins, and not all NR protein allergic individuals will have problems with these foods.

A study of binding patterns of IgE antibodies from the blood sera of individuals, who were not allergic to NR proteins but who had reactions to fruits, supported this. The study findings also showed that multiple bindings could occur between NR proteins and IgE from many who reacted to extracts of fruits but not to NR gloves. On the other hand, more specific and fewer bindings to NR protein were observed by those who were skin tested positive to NR glove extracts.

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Corn starch on gloves is known to act as a lubricant to facilitate ease of donning. However, in the case of NR gloves with high content of extractable allergenic proteins, the corn starch has been shown to have the ability to absorb these soluble NR proteins during the glove manufacturing process. As these fine powder particles can easily detach from the glove during the glove donning or doffing, they form a suspension of aeroallergens in the air. Inhaling or digesting this powder can cause Type I hypersensitivity allergic reactions. A study has shown that merely by switching to powder-free NR gloves from powdered NR gloves, these NR aeroallergens can be completely removed in the healthcare setting. With this change, sensitised healthcare workers are able to remain at work by using non-NR gloves, indicating that these practical measures can prevent the occurrence of NR protein allergy among healthcare workers. In another study, it was found that the number of powdered NR gloves decreased from 100% in 1994 to 10% in 2005. This decrease has caused a virtual disappearance of new NR protein allergy cases among German healthcare workers as shown in Figure 4. With continuous effort by the NR glove manufacturers to reduce the extractable proteins in NR gloves, the prevalence of NR protein allergy has recently been reported to be low even for the high-risk groups such as children with spinal dysraphism.

In view of the risks in causing possible adverse effects from the powder in powdered NR gloves, effective 18 Jan 2017, the US FDA has banned the use of powdered medical gloves in healthcare settings.

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Figure 4: Non-sterile NR examination gloves in all German acute care hospitals plus incidence of suspected cases of NR-induced occupational asthma and contact urticaria per 1,000 insured healthcare workers in private and church-run acute care hospitals from 1996 - 2005

NR proteins, especially from gloves with high content of extractable proteins and powder, are believed to transfer from the gloves when in contact with food during food handling. However, studies have shown that the extent of such transfer, if any, depends on the gloves used and the conditions of the contact surfaces of the food concerned.

A study has showed that no glove proteins were transferred to dry non-sticky food whereas the amount of proteins transferred to moist food depends on the extractable protein (EP) or antigenic protein (AP) content of the glove surface in contact with food. When low-protein NR gloves with an EP content <60 µg/dm² or AP content of <1.5 µg/dm² was were used, no measurable amount of proteins was found to transfer to even a moist nitrocellulose membrane which was used to simulate food with high binding affinity for proteins. Only NR gloves with a higher AP level of >10 µg/dm² were found to transfer detectable amount of proteins to foods such as tomato and cheese. As such, NR gloves, especially the powder-free gloves, with EP of <60 µg/dm² and/or AP <10 µg/dm² have much lower risk in causing adverse reactions to sensitive individuals when used for food handling. The findings thus demonstrated that transfer of extractable proteins could can occur when gloves with high EP content are used in food handling, and when food contact surfaces are moist. Such transfer is likely to be insignificant when gloves with low EP are used.

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Currently, there are several materials used for manufacturing medical gloves. The major ones which are used in large quantity include NR, carboxylated acrylonitrile butadiene copolymer (nitrile rubber), polychloroprene (chloroprene rubber), and synthetic polyisoprene, as well as polyvinyl chloride (vinyl). Other rubber materials such as styrene-isoprene block copolymer, polyurethane, polyethylene, and other copolymers can also be used. In addition, other elastomers such as polyvinyl alcohol and butyl rubber are also used for manufacturing chemical-resistant gloves. Among all these glove materials, it is acknowledged that NR has the following superior properties:

1. NR gloves have superior barrier properties due to their durability (good tensile strength), high tear resistance, good elasticity coupled with the softness to provide good fit and comfort, which are critical for medical gloves and are important features required when the gloves are used for long hours such as surgical procedures, to reduce hand fatigue.
2. They possess the unique ability to reseal when the NR gloves encounter needle punctures, thereby providing additional barrier protection against transmission of infectious pathogens. This is well demonstrated by a study showing that unlike vinyl and nitrile gloves which indicated significant viral leaks when punctured with an injection needle, NR gloves, on the other hand, could “self-reseal” resulting in significantly less viral penetration as observed during laboratory tests. Figure 5 shows the micrographs of the punctured gloves where needle cuts for nitrile and vinyl gloves remained open compared with NR gloves which were found to be sealed.



[Reference]

• Mylon P., Lewis R., Carré M.J., Martin N., Brown S. “A study of clinicians’ views on medical gloves and their effect on manual performance” Am. J. Infect. Control 2014; 42, 48-54
• Hasma H., Othman A.B. and Fauzi M.S. “Barrier Integrity of Punctured Gloves: NR Superior to Vinyl and Nitrile” J. Rubb. Res. 2003; 6, 231-240




Punctured NR Glove

Punctured Vinyl Glove

Punctured Nitrile Glove
Figure 5: Electron micrographs of rubber gloves punctured with 26 gauge needle


A more recent study further demonstrated that needle-punctured NR gloves could substantially reduce the penetration of Escherichia coli bacteria when tested under repeated stretching conditions as shown in Table 4.

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• Bardorf M.H., Jäger B., Boeckmans E., Kramer A., Assadian O. “Influence of material properties on gloves’ bacterial barrier efficacy in the presence of microperforation” Am. J. Infect. Control. 2016; 44, 1645-1649.

Table 4: Bacterial penetration of gloves punctured with 23 gauge needle (0.6mm)

Gloves	Quantity of bacteria recovered (natural log)*	Volume of bacteria penetrated (µL)
Nitrile Examination Glove 1	1.05	770
Nitrile Examination Glove 2	1.07	345
Nitrile Examination Glove 3	1.35	770
Nitrile Examination Glove 4	0.72	305
NR Examination Glove 1	18.90	0
NR Examination Glove 2	18.76	0
NR Examination Glove 3	2.53	55
Polychloroprene Examination Glove	2.09	10
Polychloroprene Composite Examination Glove	2.67	20
NR Surgical Glove 1	18.50	0
NR Surgical Glove 2	20.91	0
Thermoplastic Surgical Glove	22.27	0
Note: The initial bacteria concentration varied as the quantity was measured by volume

3. From the manufacturing perspective, NR gloves are much easier to make than synthetic rubber gloves. This is because:
1. NR latex has better wet gel strength than synthetic latexes, which allows easy beading process to be carried out at the cuff and drying without multiple temperature zones.
2. NR latex has a longer shelf life than synthetic latexes.
3. NR latex can be fully prevulcanised in latex state which has so far not been achieved in synthetic latexes.
4. NR latex has a longer latex pot life than synthetic latexes.
4. Of all the glove materials available commercially, only NR from Hevea Brasiliensis is a plant- based, sustainable and environmentally-friendly material. Although other plant-based rubbers such as that from Guayule shrubs are also available, they are not widely used. Unlike all synthetic substitutes derived from petrol chemicals, NR gloves are biodegradable. Furthermore, NR gloves are produced with less carbon foot-print and therefore are more environment-friendly.

1. The oil resistance and ozone resistance properties of NR gloves are not as good as those of polychloroprene and nitrile gloves. Therefore, depending on the extent of oil and fat exposure, it is advisable to change NR surgical gloves at least once after 90min of use.
2. NR gloves have a slightly lower puncture resistance than nitrile gloves when tested against rounded probes using the ASTM F 1342 method. However, regardless of materials used, there is no difference in puncture resistance needle as outlined in the ASTM F2878 method.
3. The quality of raw latex could vary somewhat being influenced by several factors such as weather, soil conditions and “wintering season”. However, with good experience in handling NR latex, it is not difficult for one to adjust some process parameters to meet production requirements. The use of commercial prevulcanised latex could also eliminate such variation.
4. From the manufacturing perspective, it is difficult to make accelerator-free NR gloves, probably due to the presence of a large quantity of non-rubber materials making the system complex.

Commercial cultivation of rubber trees started in Malaysia after the first batch of nine young rubber trees were planted in Kuala Kangsar, Malaya (now Malaysia) in 1877. Extensive research and development efforts had subsequently made Malaysia the number one NR-producing country in the world until the 1990s. Due to the progress of industrialisation, the volume of raw rubber exported from Malaysia has gradually declined over the past 25 years. However, with the accumulated knowledge in the raw material over a century, Malaysia is now the world’s largest producer and exporter of rubber gloves with a 64% global market share. The strong competition among the glove manufacturers has also led to the significant improvement in production efficiency through automation and innovation. This has also driven product quality to a higher level and diversification of products. The ecosystem for the glove industry also plays a significant role in maintaining Malaysia as a global glove powerhouse. To maintain the quality of the products, Malaysia has introduced the Standard Malaysian Glove (SMG) scheme where the NR gloves are certified to meet stringent specifications. Furthermore, to cater for NR protein allergic individuals, Malaysia is also the largest manufacturer and exporter of nitrile gloves.

Medical gloves are one of the essential and important medical devices used in healthcare facilities worldwide as they are one of the major means to control the spread of harmful infections. NR gloves have been used for this purpose for many years, and have been acknowledged to possess many superior properties that synthetic glove manufacturers are trying to achieve. These include in particular their very effective barrier protection against transmission of viruses, bacteria and other infectious pathogens; as well as their good tensile strength for durability, outstanding elasticity, good comfort and fit, and good puncture resistance with high tear resistance. Although synthetic polyisoprene can provide a similar fit and feel, the material cost is several times higher than that of NR. Moreover, the tear resistance of synthetic polyisoprene gloves is inferior to that of NR gloves. NR gloves also possess the unique ability of being able to reseal when punctured by sharp needles, thereby providing additional barrier protection against transmission of infectious pathogens. Furthermore, they are a plant-based material from the Hevea trees, and more importantly, are biodegradable unlike synthetic gloves. Hence, NR gloves are very environmental friendly.

The awareness of NR protein allergy in the late 1980s and 1990s had caused much concern among users of NR gloves. The crisis was brought about by the use of an older generation of NR gloves with high contents of extractable proteins and excessive powder. The advancement in glove manufacturing by the glove industry, especially in Malaysia, has today addressed the issue, via the production of improved low-protein, low-powder or powder-free gloves, which are low risk to NR protein allergy. The use of these gloves has in fact, been reported to have drastically reduced NR protein sensitisation and allergy in work places. As for the already sensitised and allergic individuals, it is recommended that they practise NR protein avoidance, and opt for the use of NR protein-free-synthetic substitutes, such as nitrile gloves which have also good barrier like those of NR.

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