This article was first published in 听
Until recently, I had not given any thought to hair extensions, although I was once in a salon where I was amazed at the variety of these products. They were to be found in every possible length, shade and style, made either of real hair or of various synthetic fibres.听
I recently came across a paper in the peer-reviewed journal Environment and Health called Identifying Chemicals of Health Concern in Hair Extensions. The researchers subjected 44 samples to analysis and detected 169 chemicals, including 48 that appeared on hazard lists. These included dye components, phthalates that make synthetic fibres soft and pliable, tin compounds that stabilize polyvinyl chloride (PVC) polymers as well as some pesticide residues. The researchers suggest that hair extensions may pose a risk because they are in constant contact with the skin, present possible hand-to-mouth contact and their volatile components can be potentially inhaled.
What the researchers did not do was test for any of these chemicals in the blood or urine in the people using hair extensions.听
Also, critically, there is the difference between hazard and risk. 鈥淗azard鈥� is the potential to cause harm; 鈥渞isk鈥� is the likelihood that harm will occur after dose, mode of exposure (inhalation, ingestion, skin contact) and extent of exposure are taken into account. Carbon monoxide, for example, is deadly when inhaled in a closed garage but is quickly diluted outdoors. Alcohol is toxic when consumed at a high dose but not in a glass of wine. Apple seeds contain cyanogenic glycosides that can release cyanide but swallowing a few when eating an apple presents no risk. (It would be unadvisable to consume a cup of apple seeds.)
It is difficult to estimate the number of chemicals to which we are exposed every day, but it could be up to 100,000, the vast majority of which occur naturally. More than 1,000 individual compounds can be detected in a cup of coffee, including acrylamide, furan and polycyclic aromatic hydrocarbons, all identified as carcinogens in laboratory studies, yet we know that coffee does not cause cancer.听
The doses of these chemicals are extremely small and are easily handled by the body鈥檚 detoxicating enzymes. Fruits and vegetables contain thousands of compounds. Some, such as solanine in potatoes, can be labeled as potentially toxic, while others may be metabolized into biogenic amines, like histamine or carcinogenic nitrosamines. Cooking produces numerous compounds, including acrolein, heterocyclic amines and advanced glycation end products, all potentially toxic if the dose is high enough.
Then there are thousands of compounds that can find their way into our body from tap water, toothpaste, cleaning products, cosmetics, medications, fragrances, clothing, plastics and food packaging. There are about 14,000 used in food packaging, of which 3,600 have been detected in samples of human blood, hair or breast milk. We live in a complex chemical landscape in which many hazardous chemicals can be identified but risks are notoriously difficult to evaluate, especially considering that mixtures can behave very differently from individual compounds.
There are three standard rules of toxicology. To start with, there is the classic 鈥渙nly the dose makes the poison,鈥� generally attributed to 16th-century physician and alchemist Paracelsus. A small dose of lorazepam (Ativan) will induce sleep; a large dose will induce permanent sleep. Second rule: 鈥淎ssociation is not causation.鈥� There is an association between roosters crowing and the sun rising, but the crowing does not cause the sun to rise. The third rule is that there are exceptions to the first two rules.
The notable exception to the first rule is the 鈥渘on-monotonic response,鈥� meaning that increasing the concentration of a chemical in the body does not produce a steadily increasing effect. A low concentration may cause a strong biological reaction, but a higher concentration gives less of a response. This seems to be the case for the so-called 鈥渆ndocrine disrupting chemicals鈥� that mimic hormones such as estrogen, or block the action of the male hormone testosterone. Bisphenol A (BPA), used to make polycarbonate plastics and epoxide linings for cans, is a weak estrogen mimic. Phthalates used as plasticizers and fragrance enhancers in perfumes have anti-male hormone effects. Hormones function at extremely tiny concentrations and can be disrupted by equally tiny concentrations of chemicals. At these tiny concentrations, they either block or activate receptors on cells, but as their concentration increases, receptors become less sensitive, and then at somewhat higher concentrations, detoxicating enzymes kick in and destroy the invaders. The dose response curve looks like an inverted 鈥淯.鈥�
Conversely, there are chemicals that have an effect known as 鈥渉ormesis,鈥� in which there is a beneficial effect at a low dose and a harmful effect becomes apparent as the dose increases. Vitamin A is a classic example. It is essential at a low dose for vision, immunity and cell differentiation, but at a higher dose it causes liver damage, birth defects and bone loss. Hormesis leads to a 鈥淯鈥� shaped dose-response curve.
The endocrine-disrupting chemicals that are present in our environment 鈥� such as BPA, phthalates and the perfluoro alkyl substances (PFAS) found in food packaging, fabrics and upholstery 鈥� are of particular concern because they can be detected in the blood at concentrations that are on the rising slope of the non-monotonic response curve. Phthalates, for example, have been linked to male fertility problems, obesity and even heart disease at low doses.听
One 2018 study attributed 13.497 per cent of all cardiovascular deaths among individuals aged 55-64 globally, a total of 356,238 deaths, to di(2-ethylhexyl) phthalate (DEHP) leached from plastics. These researchers need a course in the proper use of significant figures because reporting what is clearly an estimate to three decimal places is ridiculous. There are also confounding factors. DEHP is more likely to be found in packaged, highly processed foods, a known risk factor for heart disease.
What do we make of all this? There are thousands and thousands of synthetic and natural chemicals cruising through our body all the time. Individually, their hazards can be determined in laboratory and animal studies, but determining risk is far more challenging because the complex mixture in our blood is not equal to the sum of its parts.听
We are equipped with various detoxicating enzymes, natural antioxidants and immune-system cells that offer protection. Nevertheless, it is prudent to try to minimize exposure to known endocrine disruptors, especially during pregnancy and in childhood when endocrine systems are developing. Best bet is to push manufacturers to find alternatives to these substances.听
As far as hair extenders go, they would be way, way down my list of substances to worry about. Well below ultra processed foods.
