Is leather natural?
Another common myth about leather is that it is natural... but that raises an important question: Every piece of leather is an animal's skin, so, if it is so natural, why doesn't it rot?
Untreated animal skin does exactly what skin is supposed to do when separated from a living body; it decomposes. The only reason a leather jacket doesn't fall apart on your back is that the skin has been put through an intensive chemical transformation designed specifically to prevent decomposition.
Dr. Siobhan O'Sullivan, Senior Lecturer in Social Policy at UNSW, writes, "Turning the skin of an animal into leather is chemically-intensive and polluting."
Prior to tanning, raw skins ('hides') go through several preparation stages, including removing flesh, hairs, and fats. According to BestLeather, "once the hides arrive from the slaughterhouse or farm, the next step is to remove any scraps of flesh from them... The stages before tanning may include fleshing, preservation or curing, soaking, liming, unhairing, splitting, deliming, bating, degreasing, bleaching, pickling, and depickling."
After the preparation stages, there are two main methods that tanneries use to preserve leather: chromium tanning and vegetable tanning.
Chromium tanning
The dominant tanning method used globally is chromium (also referred to as 'chrome-tanning' or 'Cr-tanning').
Chrome-tanning is a process in which animal skins ('hides') are immersed in concentrated chromium salt baths. According to peer-reviewed studies, ¹ ² more than 90% of global leather is tanned with chromium.
The consequences for both leather tannery workers and the environment are well documented.
A 2024 peer-reviewed study published in 'Scientific Reports' found: "Wastewater sludges released by leather industries contain toxic heavy metals such as chromium, copper, cadmium, and zinc, further exacerbating pollution concerns".
"Employees engaged in the tanning and finishing of leather are potentially exposed to numerous carcinogens."
A 2008 peer-reviewed study titled 'Occupational health risks among the workers employed in leather tanneries at Kanpur' reported: "An important health risk factor for the tannery workers is occupational exposure to chromium... The workers on exposure to leather dust... exhibited a higher mean concentration of urinary and blood chromium... Professional exposure to Cr (Ш) increases the risk of dermatitis, ulcers and perforation of the nasal septum and respiratory illnesses as well as increased lung and nasal cancers."
A 2025 peer-reviewed study titled 'Occupational and Non-Occupational Exposure to Chromium Induces Oxidative Stress and DNA Damage in the Population Near Kanpur Tanneries' found: "Cr [chromium] exposure at work affects millions of individuals globally, causing significant problems such as carcinoma of the lungs, pancreas, and nasal region, which are among the tumors associated with prolonged exposure to Cr... it contributes to dermatitis, ulcerations, and nasal septal perforations... The Cr-exposed groups had elevated levels of oxidative stress and DNA damage".
Vegetable tanning
Vegetable tanning uses tannins extracted from plant materials such as tree bark, leaves, and roots.
Although this sounds natural on the surface, the purpose of tanning is to take something biodegradable (an animal's skin) and preserve it. Tanning is a process that uses chemicals to transform something organic into something inorganic, preventing it from decomposing as it would in nature.
Carl Friedrik (an international premium bovine leather goods brand) outlines the steps of the vegetable tanning process:
"Curing: the hides are salted to prevent bacteria from growing.
Liming: to remove hair and fat residues, the hides are soaked in milk of lime.
De-liming: to lower the hides' pH level, they are soaked in another chemical solution.
Tanning: over the course of 30-60 days, the hides are regularly moved into different drums filled with tanning solutions of varying concentrations.
Drying: the hides are removed from the drums and dried over a few days.
Treatment: the leather is oiled, stretched, trimmed and measured. Depending on how the leather is to be used, other finishing treatments can also be applied."
Despite being marketed as eco-friendly, peer-reviewed studies document significant environmental and health concerns associated with vegetable tanning.
A peer-reviewed study on "leaching of pollutants from vegetable tanning residue" found, "There was a continuous release of pollutants from the vegetable tanning residue." The researchers specified, "The concerned pollutants were pH, Chemical Oxygen Demand (COD), tannin,sulfate and chloride concentration."
A peer-reviewed study titled 'Measuring the Environmental Footprint of Leather Processing Technologies', which measured carbon, water, and energy footprints across 12 tanneries in 7 countries, concluded: "No significant differences were found in the [environmental] footprint of vegetable and chromium leather processes".
A peer-reviewed vitro study using human liver cells in laboratory conditions to evaluate the DNA-damaging effects caused by bovine leather tanning found: "The highest level of DNA damage was observed after exposure to the leather sample processed with vegetable tanning... followed by... chrome tanning". The researchers noted, "The effects measured in the exposed cells indicate that the leaching of potentially genotoxic chemicals from the same surface is variable and was highest after vegetable tanning, followed by... chrome tanning."
