The news broke recently that nail polish can harm your health (again!). This time, it’s triphenyl phosphate, a chemical used in nail polish to increase flexibility – it’s also used as a fire retardant. It’s a potential endocrine disruptor (“it could make you fat!”), and was found to be increased around seven-fold – or so it was reported. In particular, the Environmental Working Group (the people behind the “sunscreen is toxic” story every summer) has been the source for most of these articles.
News sites are notoriously bad at reporting scientific studies, so I went back to the source to read the full text of the original paper from Mendelsohn et al.. Unfortunately it’s behind a paywall, so I can’t link you to the full text, but I’ll provide a summary instead.
What’s TPHP and what are its effects?
Triphenyl phosphate (TPHP) is a chemical used in plastics to improve flexibility and as a flame retardant. A handful of animal studies and in vitro studies have suggested that it could be an endocrine disrupter which affects your hormones – in particular, it could potentially affect reproductive health and lipid metabolism (that’s where the “nail polish makes you fat” headline comes from). A couple of epidemiological studies in humans have also found correlations between TPHP and decreased sperm counts. However, all of this is far from conclusive evidence, and as you’ve probably gathered from being on the internet in the past 5 years, it’s almost like every chemical ever can be linked to endocrine disruption if you try hard enough.
In the body, it’s metabolised quickly to a related chemical, diphenyl phosphate (DPHP), and excreted in the urine.
What studies were performed?
The paper reports two main studies, performed with a nail polish containing 0.97% TPHP by weight.
- 16 female students removed any nail polish they were wearing 72 hours before the experiment.
- They then collected one sample of urine (T1).
- 24 hours later, they painted their nails with two coats of the same clear polish.
- 2 – 6 hours later, they collected another urine sample (T2).
- 10-14 hours later, they collected a third urine sample (T3).
- 10 females removed nail polish they were wearing 72 hours before the experiment.
- All urine was collected in the study, either for 24 hours (6 subjects) or 48 hours (4 subjects).
- The participants first collected urine for 24 hours, during which they didn’t use nail polish (Control Phase).
- The subjects were divided into two groups:
- Half painted their nails with 2 coats of the polish (Nail Painting Phase).
- The other half painted synthetic nails attached to latex gloves, then waited an hour before throwing out the gloves (Glove Painting Phase).
- After waiting at least 7 days, the groups swapped over (this is what’s known as a crossover study, where each person essentially acts as their own control).
The urine samples were analysed for DPHP content. To account for dilution effects (e.g. if one person drinks a lot of water), the urine samples were corrected for specific gravity (SG).
I don’t have a comprehensive background in designing biological studies or in statistical analysis, but nothing really rings any alarm bells for me (but I’m happy to be corrected if anyone spots any shifty manipulation!).
Does wearing nail polish increase the amount of TPHP in your body significantly?
In terms of concentration, yes, it appears so, in both experiments – to quote the study, “nail polish is a likely source of exposure to TPHP and that use may result in exposures substantially greater than background levels.” (Background means in the absence of nail polish.) It’s worth noting that you have to wear the nail polish, not just inhale it – Glove Painting didn’t cause the same increase. As well as the hard numbers, it’s pretty apparent, visually, from the graphs of urine DPHP from Cohort 2 (which I’ve painstakingly re-graphed to hopefully avoid any awkward debates about Fair Use).
There’s no tomfoolery with the scale of the axes – all the graphs are scaled the same. There are a couple of blips in the data (the couple of randomly high DPHP samples in the control phase and the high DPHP sample in the glove painting phase that sticks out like a sore thumb) but I think it’s pretty hard to downplay the trend here.
But is it significant in terms of physiological effects?
In other words, will this be enough to affect your health? The annoying thing is… we don’t know. The amounts we’re talking about here are tiny – we’re looking at millionths of a gram here. 6 times a tiny amount is still a tiny amount, and although tiny amounts of toxic substances can be toxic (see for example, botox), tiny amounts of other substances can be fine (see e.g. the tiny amounts of mercury in vaccines, lead in pretty much everything). There isn’t enough data on the effects of TPHP in humans to say anything conclusive.
As the researchers wrote:
“More research is needed to determine whether our reported levels of exposure to TPHP from nail polish use post a risk to human health.”
Should I be worried/throw out my nail polish/cry quietly in a corner because TPHP is inescapable?
For now, I would say no – until there’s evidence that these tiny changes will actually affect your health in any meaningful way, there really isn’t any cause for alarm.
- DPHP is found in low concentrations in pretty much everyone’s urine. Hence, even if you were going to get rid of TPHP-containing nail polish, it won’t help much. Additionally, the researchers measured the TPHP in 3 polishes which didn’t list TPHP in the ingredients list – they found it in 2 of them (at 0.49% and 0.61%). Looking at the ingredients list doesn’t help here, it seems.
- The study hasn’t been reproduced, and the sample sizes are quite small, the amounts we’re talking about are tiny and there’s close to no evidence that these tiny changes do anything significant to you.
- The animal studies showing the adverse effects of TPHP use way larger amounts, and exposure was much more intense – rats were fed TPHP daily, for example, and zebrafish were literally swimming in water laced with TPHP.
- The fact that it’s being metabolised and excreted so quickly is actually encouraging – it’s being efficiently processed by your body’s natural detoxifying systems.
- All in all, eliminating TPHP-containing nail polish is really, really far down the list of impactful lifestyle changes you can make to improve your health.
- News sites keep using the phrase “fire retardant” like it’s a scary term – is it, really? Water is an amazing fire retardant too.
- Of the (rather few) polishes that the researchers tested, clear polish had higher levels of TPHP than coloured polish.
- Nails aren’t very permeable to chemicals, generally. The researchers report that they’re unsure whether TPHP enters the blood through the nails or the skin around the nails or something else (like nail biting) – my money is on the skin around the nails (i.e. not being able to colour within the lines when nail painting).
- It’s estimated that adult women paint their nails on average once a week – really?! I paint my nails once a week and I’m a card-carrying addict… maybe the swatchers bump up the average for the rest of us? Also, it’s been estimated in previous studies that on average, 0.3 g of nail polish is used per application.
- This write-up by the executive director of the EWG, Heather White, is surprisingly full of scaremongering and irrational thinking. I was actually starting to warm up to the EWG since they had a toxicologist on this paper, and the paper itself seems pretty reasonable in its conclusions… but then I read this post and stopped wondering if I should start taking them seriously. Key tinfoil highlights:
- “The conclusion is inescapable: any girl who paints her nails stands a chance of coming into contact with a potential hormone disruptor.” (Yeah… breathing does that too. DPHP is found in up to 90% of urine samples.)
- “How can the cosmetics industry get away with adding TPHP to popular products? The federal laws meant to regulate toxic chemicals in cosmetics and other consumer products are broken.” (TPHP is a toxic chemical now?)
- “The “mani-pedi” culture endangers salon workers and manicurists, too.” (It does… but TPHP is the least of their worries, so why are we discussing this here again?)
- Of course, the EWG have now started a premature petition to remove TPHP from nail polish, reaffirming my lack of faith in their ability to science and use common sense. I mean, really? After all the sensible “be alert but not alarmed” conclusions from the authors of the paper? And wasn’t TPHP added to polish to replace phthalates, after a scare campaign about them being endocrine disruptors took hold? Sure, let’s move onto a new plasticiser with even more poorly understood health effects!
E Mendelsohn, A Hagopian, K Hoffman, CM Butt, A Lorenzo, J Congleton, TF Webster and HM Stapleton, Nail polish as a source of exposure to triphenyl phosphate, Environmental International 2016, 86, 45-51.
Wellek S, Blettner M. On the proper use of the crossover design in clinical trials: part 18 of a series on evaluation of scientific publications. Dtsch Arztebl Int. 2012;109(15):276-281. doi:10.3238/arztebl.2012.0276
Meeker JD, Stapleton HM. House dust concentrations of organophosphate flame retardants in relation to hormone levels and semen quality parameters. Environ Health Perspect. 2010;118(3):318-323. doi:10.1289/ehp.0901332
Meeker JD, Cooper EM, Stapleton HM, Hauser R. Exploratory analysis of urinary metabolites of phosphorus-containing flame retardants in relation to markers of male reproductive health. Endocr Disruptors (Austin). 2013;1(1):e26306. doi:10.4161/endo.26306