Even so, the general consensus was still that starch did not present a hazard to glove users, but in the mid 1970's a series of experiments were performed which showed that delayed hypersensitivity to starch could be induced in guinea pigs. Human patients were also shown to have developed hypersensitivity to starch Citation:grant davies espiner 1982 but reported cases are rare. Many users believe the reactions they experience from a latex glove are due to the powder, but this is rarely the case. The majority of glove reactions are Type IV (delayed-type) allergy, usually from accelerators. Immediate-type allergies occur less frequently, and are usually initiated by latex proteins, but accelerators have also been shown to induce glove-related immediate-type allergies. Citation:Heese Hintzenstern Peters Koch Hornstein 1991 Although glove powder has been reported to be the cause of several cases of immediate-type reactions, Heese et al Citation:Heese Hintzenstern Peters Koch Hornstein 1991 believe that the observed incidences have been due to the presence of proteins in the powder. They also note that epichlorhydrin and sorbic acid (found in some glove powders) are known Type-IV allergens. Glove powder can also provoke irritant reactions by mechanical means, especially in atopic patients.
The usual method of applying the powder is by immersing the gloves into a slurry of the powder. It is now clear that during this process proteins can be leached from the latex and deposited in the slurry mix. Citation:Esah Yip Mok Ng production of natural rubber low extractable protein 1994 The advantage of this is that the extractable protein in the glove can be reduced further. However, there is a danger of protein build up in the slurry tanks themselves, which can lead to deposition of protein back onto the gloves.
Of particular concern is the observation that the starch binds the allergenic latex proteins. Thus corn starch powder does not generally cause an allergic reaction on its own, but by binding with the latex proteins it provides a vector for transferring the protein to staff and patients as follows:
Aerosolisation of the powder and subsequent inhalation - when users don a pre-powdered glove, the powder can be released into the air where it can be inhaled. The bound protein can cause a range of allergic reactions such as asthma and conjunctivitis.
Mechanical abrasion of the users skin - the starch particle can abrade the users skin, transferring the bound protein directly into the abrasion.
Transfer of the powder to the body cavity of the patient - complete removal of powder is extremely difficult, and medical staff may transfer the powder-protein complex directly into the patient during treatment.