Allergy, in its strictest definition, resides in the fact that some individuals one day stop responding to a foreign substance as "normal" people, whereas they did so until now. The "normal" individual opposes to the foreign substance a defensive process that destroys it. The allergic individual adds, "in supplement", a chain of ill-considered biological reactions. These reactions lead to diseases, so-called allergic symptoms. Thus, a substance quite harmless for some may cause an allergic reaction for a sensitized person. Allergies can be classified into four distinct types, depending on the cells of the immune system involved. The allergy does not spare anyone, it is not reserved for the child and no adult is immune to having an allergic reaction past a certain age. Allergens are found almost everywhere: in the environment (pollution, climate, animals, and pollen), in food (cow's milk, eggs, pesticides, etc.), in insect bites, in certain medicines but also in cosmetics, both "cheap" and "high-end". They can also be present in the products of the leather industry. Depending on the type of allergy and its severity, the symptoms will differ. They can manifest as runny nose, eczema, burns, swelling, itching in the epidermis. The allergic reaction can also affect the respiratory tract, the oral cavity and the digestive tract.
Reactions to leather products, in contact with the skin, will generally cause a type 4 allergy; you must immediately stop wearing or using them and consult a health professional. Indeed, when an allergic reaction is suspected, it is better to consult an allergist who will identify the allergen responsible, first by studying the situation that triggered the reaction, then by additional tests, mainly on skin. The latter consist in bringing into contact with the epidermis the allergenic substances suspected of being the cause and observing the reactions of the organism. Once the substance is identified, the allergist will define a treatment, the first step of which is usually to avoid contact with the allergen.
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Raw hides are tanned to get leather. Currently, 80 to 85% of the leathers are chrome tanned. This process makes it possible to obtain excellent physic mechanical properties under optimum economic conditions. Only trivalent chromium or chromium (III) is used for tanning. However, if the tanning process is not perfectly controlled, it is possible that a part of the chromium (III) reacts and turns into chromium (VI). This substance is identified as an allergen by skin contact. There are no reliable data on the percentage of the population that is likely to react. Some publications mention figures in the order of 0.2% of the population. Annex XVII of REACh mentions the prohibition of chromium (VI) in leather since 2015. It must be below the limit fixed by the test methods (EN ISO 17025 part 1 or 2), namely 3 mg / kg dry leather.
Costume jewelery, watches, jeans buttons, belt buckles, coins, cell phones… All these objects can trigger an allergic reaction caused by the presence of nickel. This noble metal, not very sensitive to corrosion, was frequently used in surface treatment of metal parts to protect basic alloys (brass, steel, etc.). This allergy is quite widespread since it affects 10% of the world population. Women are more likely to be allergic than men, although more and more men are. This is due in particular to the current trend of piercings, but also to the intense use of electronic devices. The European community has regulated metal accessories that can release nickel since 2000. Tested according to EN 1811, metal parts in contact with the skin must not emit more than 0.88 μg of nickel per cm² per week.
It is possible to be present in leather and textiles. The European Union has not set any restrictions on formaldehyde. However this substance is regulated in leather in China (GB 20400) and in textiles in some European and Asian countries (Finland, Japan, etc.). EN ISO 17226 (parts 1 and 2) for leather and EN ISO 14184-1 for textiles allow its determination.
However, it is possible to establish another list of substances known or strongly suspected of causing allergies without being subject to legislation. This mainly concerns products triggering reactions but only on a small part of the population.
Allergenic substance in shoes, leather, clothes...
Disperse Blue 1, Disperse Blue 3, Disperse Blue 7, Disperse Blue 26, Disperse Blue 35, Disperse Blue 102, Disperse Blue 106,
Disperse Blue 124, Disperse Brown 1, Disperse Orange 1, Disperse Orange 3, Disperse Orange 37/76, Disperse orange 149, Disperse Red 1, Disperse Red 11, Disperse Red 17, Disperse Yellow 1, Disperse Yellow 3, Disperse Yellow 9, Disperse Yellow 23, Disperse Yellow 39, Disperse Yellow 49
These are mainly so-called "disperse" organic dyes, mainly used for coloring textiles. They are very present in the specifications of large retailers and brands. Their presence is determined by analyzes in accordance with DIN 54231 or EN ISO 16373 (Parts 1 to 3). The requirement generally corresponds to an extracted quantity of less than 50 mg / kg.
4-chloro-3-methylphenol (CMK), 2- (thiocyanomethylthio) benzothiazole (TCMTB), 2-octylisothiazol-3 (2H) -one (OIT), orthophenylphenol (OPP)
These substances are used for the preservation of raw hides, or at different stages of the manufacture of leather, to prevent its degradation by microorganisms, mainly molds. The 4 substances can be used as biocides to test hides and textiles (biocide regulation 528-2012). To date, only 4-chloro-3-methylphenol is allowed, the other three are under study. There is no compliance threshold when determining their presence according to EN ISO13365.
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Examples of "resin" acids contained in rosin: methyl abietate, palustric acid, dehydroabietic acid, abietic acid, pimaric acid Rosin is a natural substance mainly derived from pine resin. It is a complex substance that can contain up to a hundred different molecules, especially "resinous" acids. Present in many cosmetics, it is also found in glues as a "tackifying" agent. The experience of our laboratories shows that it is one of the most common causes of allergy triggering. Currently, its presence can be determined only qualitatively through the search for the main resin acids constituting it.
2-mercaptobenzothiazole, tetramethylthiuram disulfide, zinc dibutyl dithiocarbamate
These molecules belong to three major families: benzothiazoles and analogues, thiurams and dithiocarbamates. They all contain sulfur atoms and are added to accelerate and complete the rubber vulcanization chemical reaction. These substances are in residual form.
Drometzole, acetophenone azine, 2-methyl-4-isothiazolin-3-one
/ MIT, 2-hydroxymethyl methacrylate, paraphenyldiamine, para-terbutylphenol, etc.
The list of allergens may not be endless, but it is surely very long and extends very regularly with the appearance of new materials, the progress of medicine and the evolution of reactions of the human body to environments exteriors.
CTC is frequently contacted by companies marketing consumer goods, the authorities in charge of sanitary controls or by allergists, to identify substances or verify the veracity of a hypothesis. These expertise calls on qualified personnel working on state-of-the-art techniques. Despite all these means and efforts, it is not always possible to ensure unambiguously the presence of these allergenic substances. Currently NAFSEL (National Agency for Food Safety, Environment and Labor) is conducting a study on allergens in shoes with the collaboration of CTC. More results will be available soon.
