What treatments can they undergo i natural fabrics in the production of the raw material and processing of the products? Cotton, linen, silk and wool are natural fabrics even after being transformed into fabrics or packaged into clothing? Only a transparent and certified supply chain can give some guarantees and if you know one (not that there are many) contact that one.
Given that i natural fabrics they have and retain unique and inimitable properties from synthetics, including hi-tech ones, it is not excluded that the finished products carry some traces of unwanted chemical substance and that during cultivation and production treatments and processes that are not completely harmless have been used for the environment. Let's see for example what these treatments can be.
For the cultivation of cotton, pesticides and fertilizers are widely used. The seed is treated with fungicides but the plant is vulnerable to attacks by a wide variety of harmful insects which gradually become increasingly resistant to insecticides. This is why biological control has also been introduced in India, despite continuing to use products similar to DDT which are often banned in many other countries around the world.
Among other vegetable raw materials for the production of natural fabrics, flax is also treated with pesticides, but to a lesser extent because its growth cycle is shorter than that of cotton. Once harvested, the cotton is chemically bleached, treated and dyed. The same is done with linen that was traditionally left in the fields to naturally whiten under the action of the sun and rain (today practically nobody does it anymore).
Not all treatments are harmful, but some are. The 'sanforized' cotton is simply pre-shrunk and the 'mercerized' cotton is treated with a non-toxic solution to improve its strength and color. The cotton and linen of the fabrics defined as 'easy to treat' or 'crease-resistant' they are instead processed with a chemical substance which is usually formaldehyde resin. The natural fabric treated so it remains crease-resistant, but sensitive people should avoid contact with fabrics who have undergone these treatments (not always indicated on the label).
Wool and silk are natural fabrics of animal origin and consequently the problem of pesticides does not arise, however even silk can be treated with formaldehyde to prevent it from getting stained with water. Often, however, a hand wash with soap and water is enough to eliminate it, which is advisable before wearing it for the first time.
A separate chapter concerns color. Chemical dyes of cotton, linen, silk and wool or the mordant used to fix the color can be toxic. Having to choose, it is good to bet on natural fabrics with light colors because the fabrics with rich and bright colors, which fade a lot when washed, facilitate absorption through the skin.