Retailers’ guide to footwear allergies

The causes of allergic reaction to materials used in footwear, and how retailers can assist consumers.

by Rebecca Shaw

On rare occasions, footwear can be linked with allergic reactions. The intimate contact that occurs between the foot and the interior of a shoe means that the possibility of an allergic reaction is more likely with footwear than with some other items of clothing.

An allergic reaction to an item of footwear does not necessarily mean that the product is inherently faulty. Before assuming that an irritated area is caused by an allergy, the footwear should be examined to determine if the irritation may have been caused by something physical in nature – for example, by ill-fitting footwear.

If a consumer develops a reaction to an item of footwear, a medical opinion is needed to determine if this reaction is allergic in nature. A dermatologist can perform patch tests against standard reagents to identify the allergen of concern. Some allergens may only affect a small proportion of the population. However, the effects of this allergic reaction can be uncomfortable, with symptoms including skin inflammation, itching and blistering. The following are some common allergens which may be present in footwear or footwear components.

PTBF resin

Para tertiary butyl phenol formaldehyde (PTBF) resin may be found in some polychloroprene adhesives. Resin rubber and moulded rubber soles may be secured using polychloroprene adhesives. If a consumer has a PTBF allergy, it is best to avoid this type of soling. Selecting unlined footwear or footwear containing loose insocks (where an adhesive will not have been used), with a polyvinyl chloride (PVC), thermoplastic rubber (TR/TPR) or polyurethane (PU) sole would be a wise decision.

Chrome-tanned leather

Chromium salts (chromium sulphate) used in the tanning process can cause chromium sensitivity in a small number of individuals. This sensitivity may cause contact dermatitis, which is an inflammation of the skin characterised by redness, itching and blistering. A common use of chrome-tanned leather is in footwear uppers and linings, as well as handbags, belts and furniture upholstery.

It may be best for anyone with a chromium allergy to avoid footwear with leather uppers, as the vast majority of such leathers are chromium tanned. There are an increasing number of chromium-free leathers being marketed, especially in the automotive industry and for babies’ shoes. Therefore, it may be possible to select chromium-free footwear from specialist suppliers.

Generally, for people with chromium sensitivity, footwear containing synthetic materials (textile or coated textile uppers and linings) is advisable. It is unlikely that synthetic linings and insocks would provide an effective barrier that would prevent an allergic reaction on the foot if chrome-tanned upper leather is present.

Sole leathers are traditionally vegetable-tanned, but may still contain small amounts of chrome. Furthermore, some speciality sole leathers – such as ballerina shoes – are chrome-tanned, and so will contain appreciable amounts of the chrome allergen.

Natural latex rubber

Natural rubber is produced by tapping rubber trees to release latex. It is the extractable proteins in the latex which can cause allergic reactions. This type of allergy is most common in people who wear natural rubber latex gloves, such as health care workers, where an estimated 10-17 per cent are affected by a latex allergy. There are two types of allergic reaction: ‘Type I’, which is an immediate and possible severe reaction, and ‘Type IV’ – a delayed reaction that often results in contact dermatitis.

Type IV rubber allergy

Vulcanised rubber itself is not a Type IV allergen; it is the additives used in the vulcanisation process of rubber which can cause sensitisation. The chemicals of concern are thiurams, carbamates and mercapto (mercaptobenzothiazole). By careful selection, it should be possible to purchase footwear which contains little or no vulcanised rubber. The main use of vulcanised rubber is in solings. Therefore, it is important to select shoes with soles made from PVC, PU, TR/TPR, ethylene vinyl acetate (EVA), or leather. All of these should be free from vulcanised rubber, which can be associated with foot dermatitis through a Type IV rubber allergy.

Nickel

One of the most common allergies is to nickel. Approximately 10-12 per cent of the female population and 6 per cent of males are allergic to nickel. The high proportion of female sufferers is mainly due to women wearing more jewellery such as earrings. However, this ratio is becoming more even as fashions change. Nickel is one of the substances listed in REACH Annex XVII, Entry number 27. REACH is substantial European chemical legislation, and Annex XVII within this legislation is a list of restricted substances and their maximum limits permitted in consumer goods.

The restrictions for nickel are a maximum migration of 0.5µg/cm²/week for metal items that come into prolonged contact with the skin, and a lower migration limit of 0.2µg/cm²/week for earring piercing posts. This is due to their highly intimate contact with the body. In footwear, rivet backers, D-rings and metal trims may all be found in intimate contact with the skin, depending on the footwear design. These items should be risk assessed for their likelihood of prolonged skin contact and be tested to ensure they meet with the requirements of REACH regulation 1907/2006 Annex XVII, Entry number 27. SATRA can help members with both this assessment and testing.

Dyes

Man-made textiles such as polyester, polyamide (nylon), polypropylene and cellulose acetate fibres can be dyed using a disperse dye. Some of these disperse dyes are known to be allergenic, and cause skin irritation in people who are sensitised to such chemicals. Disperse dyes are so-called due to the nature of the dying process – the dyes are applied to the textiles in the presence of a dispersing agent. Another allergenic dye is paraphenylenediamine (PPD). This may be used to dye textiles and leathers, and can also be found as an additive in black rubbers. Consumers with these allergies should avoid footwear with dyed textile and leather linings, instead selecting footwear with white textile or undyed leather linings and insock.

Formaldehyde

The footwear materials most likely to contain formaldehyde are textiles (where it may be used as a stiffener) and leathers, where it may be present in some synthetic tannages or finishes. Even exposure to low levels of formaldehyde may result in irritation to the skin of people who are sensitised to the chemical. If formaldehyde is present at a high enough level, it is a known irritant to the general population. There are currently no maximum legal limits for formaldehyde within Europe, although it is included in many European ECO label standards. Formaldehyde is readily soluble in water and can, therefore, migrate through materials with the aid of perspiration. SATRA can help members with testing for the presence of formaldehyde.

From a customer’s service point of view, it would be beneficial for retailers to have an understanding of possible allergies, so that they can provide reasonable guidance and advice to consumers at the point-of-sale. This guidance may take the form of checking footwear labelling pictograms for materials present. As previously mentioned, consumers who suffer chromium sensitivity should avoid leather footwear (denoted by the hide symbol on composition labels). Other allergens such as Type IV rubber allergies will require more information than just the labelling pictograms. Consumers who suffer this type of allergy should avoid vulcanised rubber, so the retailer will need to check material specifications to confirm whether vulcanised rubber has been used.

Finding a cause

If an allergic reaction has been reported with footwear, a medical opinion is always advised to identify the substances that are causing the allergy. Laboratory testing may then be necessary to confirm whether these possible allergens are present in the footwear.

Publishing Data

This article was originally published on page 32 of the May 2012 issue of SATRA Bulletin.

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