Clothing is the material that spends more time in contact with the human body than any other in the home environment. The average person wears clothing for sixteen or more hours a day, with fabric pressed directly against the skin at virtually every square inch of the body except the face. It sits against the most absorptive regions of the body — the groin, the axillae, the inner arms — for the full duration of every day, and against the skin of the entire body during sleep for those who wear clothing to bed. Given this intimacy, the chemistry of what clothing is made from is not a trivial consideration. It is a direct and continuous environmental health input to the body’s largest organ.
The dominant fibers in contemporary clothing — polyester, nylon, acrylic, spandex and its variants, and the blends that combine them — are petroleum-derived synthetic polymers. Their adoption accelerated rapidly from the 1950s onward as the petrochemical industry scaled production and drove costs below those of natural fibers. Today, synthetic fibers account for approximately 60 to 65 percent of global textile production, with polyester alone representing more than half of all fiber produced globally. Most people alive today have spent the majority of their lives with petroleum-derived polymers as their primary material of skin contact.
WHAT SYNTHETICS CARRY
Synthetic fibers themselves are not the only chemical component of a synthetic garment. The dyestuffs used to color synthetic fabrics — azo dyes, disperse dyes, and reactive dyes formulated specifically for synthetic polymer bonding — include compounds that have demonstrated skin sensitization, contact dermatitis triggering, and in some cases systemic effects in research on occupational and consumer exposure. Azo dyes, which constitute the majority of synthetic textile colorants, can release aromatic amine compounds including some classified as carcinogens by the International Agency for Research on Cancer when they degrade on skin or in wastewater.
The finishing chemicals applied to synthetic fabrics add another layer to the chemical inventory. Wrinkle-resistant finishes on polyester-cotton blends use formaldehyde-releasing compounds as their chemical mechanism. Moisture-wicking and water-repellent finishes on performance fabrics frequently use fluorinated compounds — including some in the PFAS family — that provide their function through fluorocarbon surface chemistry. Antimicrobial finishes, as discussed in the earlier article on textiles, add biocidal compounds to the fiber surface. And softening agents, antistatic treatments, and the various processing aids used in textile manufacturing remain in the finished fabric in residual quantities that contact skin with every wearing.
THE SKIN ABSORPTION ROUTE
The skin is not an impermeable barrier. It is a selective one — highly permeable to lipid-soluble compounds, moderately permeable to small hydrophilic compounds, and effectively impermeable to most large macromolecules. The chemical compounds of greatest concern in synthetic textile finishing chemistry — the aromatic amines from azo dye breakdown, the PFAS compounds from fluorinated finishes, the formaldehyde from wrinkle-resistant treatments — fall into the lipid-soluble and small-molecule categories that the skin absorbs most readily.
The absorption is not uniform across the body. The skin of the axillae, groin, and inner elbow is significantly more permeable than the skin of the back or upper arm — precisely the regions where clothing fits most closely and where sweat accumulation increases both the local temperature and the local concentration of chemicals migrating from fabric. A study measuring the dermal absorption of textile dye compounds found absorption rates in the axillary region up to twenty times higher than the same compounds applied to the forearm — the reference site in most dermal absorption studies.
Heat and sweat compound the chemistry. Elevated skin temperature dilates the capillary beds underlying the skin, increasing dermal blood flow and absorption rate. Sweat serves as a solvent that extracts chemical compounds from fabric and delivers them to the skin surface in dissolved form, dramatically increasing the concentration gradient that drives absorption. The workout in polyester athletic wear is therefore a higher-exposure event than the same garment worn at rest — the combination of heat, sweat, and elevated absorption rates that exercise produces concentrates the chemical transfer precisely when the fabric is most heavily used.
MICROPLASTICS ON SKIN
Beyond the chemical finishing compounds, synthetic fabrics shed microplastic fibers during wear as well as during washing. The microplastic shedding from fabric surfaces during normal wear — movement, friction against other surfaces, the continuous mechanical stress of ordinary activity — deposits microplastic fibers onto the skin surface and into the adjacent air. Research has found that synthetic textiles are a primary source of the indoor airborne microplastic fiber load, with indoor air microplastic concentrations consistently higher than outdoor concentrations in studies examining homes where synthetic textiles are present.
The inhalation route for airborne microplastic fibers is the primary concern for indoor air quality. But skin deposition of fibers shed from worn clothing creates an additional exposure pathway, particularly in the enclosed micro-environment between close-fitting synthetic garments and the skin surface, where fiber shedding is highest and the distance to skin is smallest.
THE ENDOCRINE QUESTION
The endocrine disruption concern with synthetic clothing centers on two specific compound classes. The first is bisphenol A and related compounds, which are used as processing aids in some polyester and polycarbonate textile components and which leach from the polymer under sweat and heat conditions. The second is phthalate plasticizers, used in the production of flexible synthetic fibers and in some textile printing inks, which have well-documented endocrine disrupting activity and which have been detected in the sweat of individuals wearing synthetic garments in controlled exposure studies.
The proximity of synthetic undergarments to reproductive tissue is the most specific anatomical concern. The testicular proximity of polyester underwear has been studied — a controversial but methodologically interesting series of studies found that men wearing polyester undergarments had measurably lower sperm parameters than those wearing cotton undergarments, with a mechanism proposed involving both scrotal temperature elevation and chemical exposure through the highly permeable scrotal skin. These findings have not been replicated at scale, but they illustrate the specificity of the anatomical concern about synthetic fabric against the body’s most chemically sensitive and reproductively significant tissue.
None of this demands the immediate elimination of all synthetic clothing from daily life. It demands the awareness that what is worn against the skin is a chemical and physical environment, that some of that environment has biological consequences, and that the choices that most affect that environment — what is worn closest to the body, what is worn during the highest-absorption situations, and what is worn during sleep — are worth making deliberately.