That is exactly why the International Association for Research and Testing in the Field of Textile and Leather Ecology created the special Oeko-Tex certificate, thanks to which we can be sure that the clothing we wear is completely harmless.
Before the certificate is granted, textiles are thoroughly checked at every stage of production; laboratories check their composition (nitrogen dyes, carcinogenic and allergy-causing dyes and pesticides are prohibited, among others), smell, volatile compound emissions, pH, resistance, etc.

Information about the certificate is usually placed on the product label, but not always, so if in doubt you should ask the manufacturer or the seller.

It is also worth knowing that apart from the standard Oeko-Tex certificate, there are also: STeP by Oeko-Tex, Made in Green by Oeko-Tex, Leather Standard by Oeko-Tex and Eco Passport by Oeko-Tex.