Standards and use for chemicals in leather production


Dr Alois Püntener*


Use and making Leather


The use of leather dates back almost as long as recorded history, protecting our ancestors when they went out to hunt. They used a lengthy and fairly sophisticated process to tan hides and skins to make them durable: if they had simply dried the skin the resulting leather would have been too hard, if they had kept it moist, the skins would have rotted and decayed. The preparation of animal skins was one of our ancestors’ first crafts, probably first carried out by women, and later, in the pre-industrial times, mostly by men.


The animal skin was not only used as jewellery and camouflage or for protection but also for tools, household items and shoes – the shoemaker was one of the most important users in early times.


These original tanners developed innovative techniques and used basic chemicals to make the skin strong, durable and fashionable. The know-how was passed on from generation to generation, and subsequent trade guilds protected the secrets of the process.


Nowadays, leather is mainly produced industrially. The technology and procedures are based on past experience and have been modified and optimized accordingly. Today, leather is used for a variety of items, including clothing, footwear, handbags, furniture, tools and sports equipment, and lasts for decades.


In the past


Hide collectors were often confronted with anthrax. An infectious disease that primarily affects herbivorous animals such as cattle, pigs, goats and sheep, it can be transmitted from them to humans. Colds could occur in the beamhouse, but wetness is not the cause of rheumatism, although wetness certainly does not have a soothing effect, rather the opposite.


Dealing with the rotting skin released an unpleasant odour and tanners tended to be housed in particular areas, near flowing water, often downstream from the city. In 1700, Italian physician Bernardino Ramazzini, who specialised in occupational diseases, reported that an accumulation of tannery waste, and particularly the smell, could be damaging to health1.


At that time the unpleasant smells from waste and untanned skins were acknowledged, although it was clear that a skin should be tanned quickly and a vegetable-tanned skin gave the leather a special odour.


The smell of leather was reminiscent of wood and nature. In fact, the tangy resin aroma of vegetable tanning agents had been recommended as a treatment for lung disorders and tanning liquor was used to treat some skin diseases.


The standard of cleanliness in European tanneries – as in many craftsmen’s workplaces – was not high, but the tannery itself was not thought to be a bad working place.


In Johann Christian Gottlieb Ackermann’s translation of Ramazzini’s work it mentions that in the Polish city of Gdansk, which had been ravaged by the plague, only the tanners’ street was not affected2. We can probably assume that washing and maybe the disinfecting effect of the tanning liquors reduced the bacteria Yersinia pestis, transmitted by the bites of fleas.


Modern-day processes


The further development of leather production is closely connected with the rise of the chemical industry. Tanning changed from the domain of the trade guilds to industrial production. The leather industry has progressed immensely from those early times. New chemicals and tanning agents, new dyes and additives for handling and finishing have been invented. As a result, leather production has continuously improved with respect to the quality of leather, environmental protection, waste minimisation and disposal, the correct use of chemicals and industrial accidents. For example, the statistics in Germany show that people working in the leather industry are not exposed to health hazards to a greater extent than the rest of the population3.


The smell


Leather production still generates by-products, which find outlets in several sectors such as fine chemicals, photography, cosmetics and as soil conditioners and fertilisers. In order to avoid unpleasant smells, the putrefactive properties of animal skin must be eliminated. This is done when hides and skins are processed immediately after slaughter or by preservation with products such as common salt4.


Vital chemicals GHS, CLP, REACH, SDS


In the hands of a skilled tannery, with recipes for good tanning liquor and softening finishing oils, outstanding quality leather can be produced. Chemicals are used throughout the process, from the soaking to remove soil and other contaminants and to increase moisture, to tanning, and all the way to the finishing stage, when the leather is treated to give its final appearance and qualities. Knowledge of chemicals is extremely important when dealing with them, not only for worker protection and proper disposal, but also for the producer of leather goods and the consumer.


The United Nations Conference on Environment and Development (UNCED) provided the impetus for the development of the Globally Harmonized System of Classification, Labelling and Packaging of Chemicals (GHS)5 with Agenda 21, which was adopted in 1992. In Chapter 19 of Agenda 21, it calls for harmonisation of the classification and labelling of chemicals. We now have a globally standardised system for classifying chemicals and labelling them on packaging and in safety data sheets. It is updated regularly so that the current status must be consulted whenever there is a reference to the GHS.


On the basis of this labelling system, Europe implemented it as CLP (Classification, Labelling and Packaging) Regulation (EC) No 1272/2008), which came into force on 20 January 2009. Substances have been classified and labelled according to the CLP regulation. This has been mandatory for all available chemicals since December 2012. It is closely linked to REACH (Registration, Evaluation, Authorization and Restriction of Chemicals) regulation, consolidated version (EC) No 1907/2006, which entered into force on 1 June 2007. Its main aim is to ensure a high level of protection of human health and the environment from the risks that can be posed by chemicals. It lays down provisions governing the manufacture, placing on the market and use of chemical substances and preparations. Chemical substances, which will be intentionally released, are also covered. Chemical makers have to demonstrate how the substance can be used safely and to communicate the risk management measures to users.


A core element of the REACH regulation is that the data transmitted to the European Chemicals Agency (ECHA) in the registration process is available to the public via an internet database6 in application of the principle ‘no data, no market’. Here one can also find the regulation of CLP, BPR (Biocidal Products Regulation), POP (Persistent Organic Pollutants), etc., and the corresponding data.


To comply with REACH, a safety data sheet (SDS) must be sent to all recipients to whom the supplier has supplied the chemical. It must include information about the properties of the substance or mixture, its hazards and instructions for handling, disposal and transport and also first-aid, firefighting and exposure control measures.


Suppliers and recipients of safety data sheets are encouraged to check that the required information is provided. The format and content of the safety data sheets are specified in REACH. A user needs to understand and read the safety data sheet and apply appropriate measures to adequately control the risks.


Annex XVII of REACH includes all the restricted chemical substances. It shows a substance or a group of substances or a substance in a mixture, and the consequent restriction conditions.


Examples of restricted, limited or investigated substances that should not be found in leather include:


           dyes that can split off carcinogenic amines, carcinogenic and allergenic dyes
           chromium VI compounds, organotin compounds
           toxic metals such as, arsenic, barium, mercury, cadmium and lead
           formaldehyde content above the declaration limit
           short-chain chlorinated paraffins (C10-C13)
           polyaromatic hydrocarbons
           alkylphenols/ alkylphenol ethoxylates
           per- and polyfluoroalkyls compounds
           dimethyl fumarate
           N-methyl pyrrolidone
           polybrominated diphenyl ether


This list is being continuously updated and should therefore be consulted frequently. It is intended to help tanners and other users of chemicals to take the necessary measures and to show that the manufacturing process does not use restricted chemicals, and that undesirable chemical substances will not be found in the end products.


Means of protection, biocide (BPR)


The global nature of the industry presents its own issues. Leather, semi-finished leather, or finished products are often transported over long distances, but in warm and wet climates this requires the use of biocide products to avoid damage to the leather. These products contain or generate active substances that defend against harmful organisms in order to prevent the leather from forming a coating or taking on an unpleasant smell from mould caused by incorrect transport or storage of the leather and goods made of leather.


The use of biocides is regulated in the Biocidal Products Regulation (BPR) Regulation (EU) 528/2012. The text was adopted in May 2012 and was applicable from September 2013. It concerns products placed on the market having biocidal products, which are used to protect humans, animals, materials or articles against harmful organisms like pests or bacteria, by the action of the active substances contained in the biocidal product.


The basic principle is that a biocidal product must be authorised before it can be made available on the market or used. This takes place in two consecutive steps. First, the active substance is evaluated and, provided the criteria are fulfilled, is then approved in a specified product-type. The second step is the authorisation of each product consisting of, containing or generating the approved active substances.


Safety data sheets (SDS) must also be created for biocides in accordance with the edification of the REACH regulation.


In Annex V to the BPR, the biocidal products are classified into 22 biocidal product-types, grouped in four main areas. The biocidal active ingredients for leather products are currently in the BPR Existing Active Substances Review Scheme for Product Type (PT) 9, ‘Protective agents for fibres, leather, rubber and polymerized materials.


Biocidal active ingredients are differentiated into existing active ingredients and new active ingredients. For biocidal products that contain existing active ingredients that were already on the market before May 2000, transitional regulations can apply.


At this time the following preservatives are often used in leather processing:


           2-(thiocyanomethylthio)-benzothiazole (TCMTB)
           4-chloro-3-methylphenol (PCMC)
           2-phenylphenol (OPP)
           2-octylisothiazol-3(2H)-one (OIT)


For products with these biocidal active ingredients, the current national legal provisions continue to apply until an evaluation by the ECHA (European Chemicals Agency). The point in time for this assessment of the active substances for the PT 9 cannot be foreseen as of now. However, this is likely to be expected within a few years.


Global industry


Social responsibility is becoming increasingly important. This refers not only to working conditions but also to wages. However, owing to cost pressures, much leather manufacturing has moved to developing economies, where about twice as much leather now comes from compared to the most developed economies7.


The industry is not free from incorrect behaviour and the damage caused to its reputation by a few bad actors cannot be taken lightly. It is simply unacceptable that, while most tanners spend huge amounts of money and time building treatment plants and protecting the environment and workers, a small minority does not, behaving as though in developing countries, similar laws are not in place.


This leads the media to make the public think the worst cases are the standard; suggesting neither the owners nor the governments are looking after workers, the environment or consumers’ health and safety.


The rules for good and safe working conditions including social behaviour must not only be regulated but enforced internationally. Otherwise, leather loses its good reputation.
One has to wonder why some leather buyers neglect tanneries that invest a lot of money in cleaning their waste, in good working conditions and in making high-quality leather. They should prefer such responsible enterprises, even if the leather is slightly more expensive.


In conclusion, it should be pointed out that the International Union of Leather Technologists and Chemists Societies (IULTCS) has the responsibility to prepare leather test methods for the International Organization for Standardization (ISO)8. It provides help and protection for the tanning industry worldwide by developing and publishing test methods that are explicitly relevant to good leather quality.


The technical work preparing and updating the ISO Standards is carried out by the three Leather test method commissions (IUC-IUF-IUP) of the IULTCS:


           IUC (chemical test methods)
           IUF (fastness test methods)
           IUP (physical test methods)

The chemical test methods also include procedures for analysing for unwanted chemicals and limit value determinations for some leather preservatives, ensuring a high level of protection for users.




Responsible tanneries all over the world recycle hides and skins to create a valuable product. They are part of the solution, not part of the problem. Chemicals are used in every step of leather production but they are stringently regulated and tanneries provide safe, clean environments in which to work. Good practice and regulation keep industry und consumer safe. With good working conditions, leather has never been reported to be harmful or to cause serious illness.




1.         Bernhard. Ramazzini, De Morbis Artificum Diatriba ("Diseases of Workers"), Modena 1700

2.         Johann Christian Gottlieb Ackermann, Abhandlung von den Krankheiten der Künstler und Handwerker, Stendal 1780

3.         Jahresbericht 2020 der Berufsgenossenschaft Rohstoffe und chemische Industrie, ISSN 2194-1122

4.         Best Available Techniques (BAT) Reference Document for the Tanning of Hides and Skins, European IPPC Bureau 2013

5.         Globally Harmonized System of Classification and Labelling of Chemicals (GHS) Eighth revised edition, United Nations, 2019


7.         World Statistical Compendium for raw hides and skins, leather and leather footwear 1993-2012, FAO, 2013

7.         Globally Harmonized System of Classification and Labelling of Chemicals, Fifth revised edition, United Nations, 2013

8.         The International Union of Leather Technologists and Chemists Societies (IULTCS) official methods of analysis for leather, published by the International Organization for Standardization (ISO) CH-1211 Geneva,


*Based on a paper provided to World Leather by Dr Alois Püntener, VESLIC, Association of Swiss Leather Chemists and Technologists