The global textile sector is enormous; in 2018 the value of the US textile sector was $78 billion and employed over 550,000 workers1. In 2017 China produced 79 billion metres of cloth2; that’s enough to go to the moon and back 100 times!
Textiles and clothes are a fundamental part of our everyday life however they also provide an excellent material for micro-organisms to grow on. Measures to prevent microbial growth on textiles and fabrics dates back to Egyptian times when mummy wraps were preserved using herbs and spices3. Since then bamboo has been used in housing structures and design in China and in World War II a range of chemicals were used to impart antimicrobial activity to tents, tarpaulins and truck covers4. Prevention of microbial attack is essential for durability of the textile, in addition to potential use in prevention of transmission of disease.
Anti-microbials have become more advanced, safe and effective since these times, however there are still concerns over their use in some products, particularly clothing. Antimicrobial textiles are classified as those textiles that have been subjected to various finished to give protection to both the user of the textile and the textile itself, without negatively impacting the performance of the product.
In this context, antimicrobial textiles should be able to inactivate a wide range of microorganisms5,6, be non-toxic and environmentally friendly, durable to repeated washes and easy to recharge in laundering or disinfection processes7. In addition, the recharging agents should be non-toxic, available at home, and compatible with laundering chemicals such as detergents or bleaching agents8.
Skin is the largest organ of the body, and the majority of textile interaction with the human body is by skin contact of clothing. Where chemicals are used to impart functionality to clothing, these chemicals can also then come into close contact with the skin, and may irritate or impact on the skin. All chemicals used on products that come into contact with the consumer have to approved in the first instance by the appropriate regulatory agency. Antimicrobials are amongst the most thoroughly regulated class of chemicals9 – safety tests such as skin absorption, acute toxicity, chronic toxicity must be performed before any chemical is approved for use10. As such, in general, the chemicals used are quite safe. Some people however may be more sensitive to these types of chemicals, or sensitivity may develop over time.
While textile dyes are the most common cause of allergic contact dermatitis, some anti-microbials have also been associated with adverse skin reactions. Anti-microbials used in textiles include:
The use of silver based anti-microbials has increased significantly over the past decade. The ability to use as nano-particles has provided for greater activity at lower concentrations9. Silver can be incorporated into textiles during the production process, or added in chemical finishing. Silver nano-particles can inhibit a wide range of micro-organisms and anti-bacterial resistance to silver is low as the mechanism of action is non-specific. Generally silver particles interfere with how micro-organisms produce energy, leading to cell death11.
Triclosan is a phenolic compound that is used across a wide range of consumer products including shampoos, deodorants and mouthwash9. It has activity against a broad range of micro-organisms and is used so widely that approximately 75% of the US population is likely to be exposed to this compound via consumer products12. Triclosan can be readily absorbed into the skin and so exposure can be by both oral and dermal routes. Triclosan inhibits micro-organism growth by weakening the cell membrane, allowing cellular constituents to leak out, eventually leading to death of the micro-organism. Anti-microbial resistance to triclosan is possible, and while this reduces the efficacy of triclosan, it also has the knock on effect of also helping the micro-organism to become resistant to other antibiotics12.
SiQAC are effective against a wide range of micro-organisms and benefit from the fact that silanes are extremely effective at bonding to other molecules, making them ideal for textile applications. The QAC part of the SiQAC compound is the part that affects the bacteria; it does this by binding to the bacteria and then removing essential parts of the cell wall. The bacteria starts to leak fluid and eventually dies13. Development of resistance to QACs has emerged due to their widespread usage, and while they are effective, their use should be restricted to essential applications14.
Zinc pyrithrione is a broad spectrum antimicrobial. Similarly to other textile antimicrobials, it is used in a wide range of consumer products, including anti-dandruff shampoos, adhesives, paints and floor coverings9. This compound can introduce zinc ions into the micro-organism, where they bind to proteins in the organism and cause its internal metabolism to malfunction. While micro-organisms do not develop resistance to zinc pyrithrione in the same way as other textile antimicrobials, its ubiquitous use on a range of consumer products does make it more likely that tougher micro-organisms may develop in response to use of this (and other) anti-microbial compounds15.
PHMB is a disinfectant and anti-microbial that is used in a wide variety of applications including cosmetics, fabric softeners, hand washes and personal care products9. Similarly to other anti-microbials mentioned already, it impacts on the membrane and causes intracellular components to leak out and cause the death of the cell. There have been no reported instances of bacterial resistance developing to PHMB, and it is recommended where long term exposure to an antimicrobial is required16.
N-Halamines are broad spectrum anti-microbial agents with good stability and regeneration properties9,17. This class of antimicrobial are halogen derivatives; halogen based antimicrobials have become more popular due to their cost-effectiveness. N-Halamines can also be used in conjunction with other antimicrobial agents, improving efficacy and reducing likelihood of resistance developing. N-halamines exert their anti-microbial activity through three main actions:
Chitosan is a polysaccharide, this means that it is made up of sugar molecules, it is a natural polymer and is considered very safe. There a number of proposed mechanisms for its anti-microbial activity including:
Chitosan is required at quite high levels to exert its anti-microbial activity and so can lead to some performance issues with the textile (such as air permeability)18.
A significant challenge for any textile finish is its durability. Textiles can be exposed to sweat for periods of time, as well as to laundering conditions, at elevated temperatures with cleaning based products. This poses a number of durability challenges for textile finishes. The finish must be fixed enough to withstand this level of treatment, however must be available enough to provide efficacy. This may cause particular challenges for some anti-microbials where contact with the microorganism may be required for effectiveness. Similarly if the anti-microbial does leach off, the textile may become ineffective and may cause skin contact irritation or contact allergy.
An allergic reaction is a hypersensitivity to an allergen, often a harmless substance in the environment. Sensitisation happens when a person is exposed to an allergen over time. This may be at low levels, and the response may be mild at first but as the allergy develops, the response will become stronger. After this occurs, even short exposures to very low concentrations can cause severe reactions10.
In terms of contact dermatitis caused by textiles, dyes are the most common cause, although biocides such as some of those listed above, have also been shown to be responsible. The main antimicrobials that have been associated with contact dermatitis are triclosan, zinc pyrithione and silver particles19. It is well recognised however that the incidence of reactions to these chemicals is quite low, with reactions being described as uncommon20-23. Triclosan was banned from use in textiles in the EU in 201424. It is currently under review in the US where it was banned from cosmetic and soap products in 201625. Both silver and zinc pyrithione are widely used, although as with many consumer products, there is a move towards anti-microbials from more ‘natural’ sources.
Concentration is key in terms of use of chemicals, both in terms of functional efficacy, but also in terms of safety for humans. Chemicals have played a transformative role in all sectors and especially so in textiles. What is crucial for companies who want to ensure as safe a product as possible for their consumers, is that limit levels are adhered to, and that this adherence can be clearly communicated to the consumer.
When someone does have chemical or allergic sensitivities, the decision of whether to purchase a particular product can be challenging to make. Being informed is a great start, but the area of chemical finishes of textiles can be quite complex. Certification Standards can often be a good way to find a signpost to products that are more suitable. Relevant Certification Standards include Oeko Tex, Nordic Swan Ecolabel, asthma & allergy friendly™ and the Global Organic Textile Standard.
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