Gym Wear Chemicals May Cause Weight Gain, Experts Warn

Treating yourself to new workout clothes can be the perfect incentive to get back in the gym and shed those extra few pounds. However, experts have issued a stark warning that many popular gym wear items contain dangerous chemicals that might paradoxically lead to weight gain.

The Hidden Dangers in Synthetic Fabrics

Clothes typically worn for exercise, from spandex crop tops to polyester leggings and nylon running jackets, often contain fibres known as endocrine-disrupting chemicals (EDCs). These substances can interfere with the body's natural hormonal balance. The materials are frequently treated with known EDCs to increase their flexibility and moisture resistance, including chemicals such as BPAs, phthalates and bisphenols.

Studies suggest that EDCs mimic and interfere with the body's hormone regulation, which can negatively impact the metabolic rate. While there are various sources of EDCs in the environment, wearing them during a workout presents additional danger. A recent study from the University of Birmingham found that sweating may significantly increase the body's absorption of toxic chemicals through clothing.

Popular Brands Under Scrutiny

Workout clothes made of plastic and treated with EDCs remain abundant on the high street. The Centre for Environmental Health, an American non-profit organization striving to protect people from toxic chemicals, found numerous popular brands selling items with high levels of BPA in 2022.

The affected brands included:

Alo Yoga
Amazon Essentials
Patagonia
Skechers
FILA
Free People
Hoka
Soul Cycle
Under Armour
New Balance

The Daily Mail has reached out to all the brands mentioned for comment regarding these findings.

Scientific Evidence Mounting

Raffaele Marfella, professor of internal medicine and microplastics at the University of Campania Luigi Vanvitelli in Naples, explored the impact of plastic exposure on mice. He told the BBC: 'We don't yet have a definitive threshold for toxicity, but we are starting to see patterns. Preliminary data from animal models suggests that chronic exposure to 10-100 micrograms of microplastics per kilogram of body weight per day can induce measurable inflammatory and metabolic changes.'

Meanwhile, a comprehensive review published in Frontiers in Endocrinology examined the consequences of human exposure to microplastics. The research suggested that the global rise in plastic production may be linked to increasing obesity rates, indicating a potential environmental connection that extends beyond diet and exercise habits.

Expert Advice on Reducing Exposure

Steve Bennett, founder of wellness app Clubwell, explained the risks to the Daily Mail: 'Most people focus on what they eat when thinking about hormonal health, but what you wear matters too. Synthetic fabrics, the polyesters, nylons and acrylics that dominate modern wardrobes, contain chemicals that can interfere with your endocrine system, the very system responsible for regulating hormones including insulin, cortisol and oestrogen.'

Bennett detailed how synthetic fabrics are petroleum-based products treated with a cocktail of chemical finishes during manufacturing. These include phthalates, BPA, formaldehyde and perfluorinated chemicals (PFCs), many of which are classified as endocrine disruptors. He emphasized that the skin is the body's largest organ and absorbs substances directly into the bloodstream. When sweating opens pores, chemical absorption increases significantly.

Research published in Environment International has shown that endocrine-disrupting chemicals found in textiles can interfere with thyroid function, reproductive hormones and insulin signalling. Bennett noted: 'For anyone already dealing with insulin resistance, which affects over 90 per cent of adults to some degree, adding another source of hormonal disruption is the last thing your body needs.'

Polyester clothing has also been shown to harbour more bacteria than natural fibres, contributing to skin irritation and chronic low-grade inflammation, another driver of metabolic dysfunction.

Practical Solutions and Safer Alternatives

Bennett offered practical steps to reduce plastic exposure during workouts: 'You don't need to overhaul your entire wardrobe overnight. Start with the items closest to your skin for the longest periods: underwear, sleepwear and base layers. These are where chemical exposure is highest. Switching these to bamboo or organic cotton makes a measurable difference.'

Bamboo fabric stands out as a particularly practical alternative. It is naturally hypoallergenic, free from the chemical treatments that synthetic fabrics require, and has inherent antibacterial properties that reduce the bacterial load on the skin. Bamboo is breathable, moisture-wicking and temperature-regulating, which means less sweating and therefore less chemical absorption for those transitioning away from synthetics. From a sustainability perspective, bamboo grows rapidly without pesticides or fertilisers, making it a cleaner crop from field to fabric.

Safer Workout Wear Options

For consumers concerned about EDCs in their workout clothing, several brands offer alternatives made with natural fibres:

Pangaia Leggings: Made with 67 per cent cotton, these might represent a safer choice for workout enthusiasts.
Airoc Shorts: These contour shorts are crafted with bamboo and organic cotton materials.
Bam Clothing Bodysuit: Originally priced at £75, this item is currently available for £35.
Organic Basics Jacket: The classic grey track jacket has been reduced from £83.
Reebok Dotty Top Sports Bra: Available in two different shades and made from cotton.
The White Company Joggers: These luxe jogging bottoms feature an elasticated waistband with tie fastening.
Earth Wardrobe Bralette: Shoppers can purchase three bralettes for £39.

The findings serve as a reminder that while workout clothes are designed to support fitness goals, their material composition may have unintended consequences for metabolic health. Consumers are increasingly advised to consider not just the style and functionality of their activewear, but also the chemical composition of the fabrics against their skin during intense physical activity.