Can toothpaste harm your thyroid?

Dec 05, 2008

Zorrilla LM, EK Gibson, SC Jeffay, KM Crofton, WR Setzer, RL Cooper and TE Stoker. 2008. The effects of triclosan on puberty and thyroid hormones in male wistar rats. Toxicological Sciences doi:10.1093/toxsci/kfn225.

Synopsis by Heather Hamlin and Wendy Hessler

A toothpaste containing triclosan
A toothpaste containing triclosan
 Triclosan, an antibacterial agent used in toothpastes, soaps and cosmetics, alters thyroid function in male rats, highlighting a potential concern for people - especially pregnant women and children.  Effects occurred at doses that people may experience, given the many diverse sources of exposure now prevalent because of triclosan's widespread use.



Triclosan is an antibacterial ingredient found in many common household products, including toothpaste, mouthwash, soap, deodorant, shaving cream and cleaning supplies. Triclosan is slowly increasing its resume, as manufacturers add it to a wider range of consumer products, such as kitchen utensils, trash bags, clothing, bedding and even children’s toys. Today it is virtually unavoidable.

Chemically, triclosan is a chlorinated, organic molecule that resembles the synthetic plastic additive bisphenol A (BPA) and the long-lived dioxins, which are formed during incomplete burning and can cause cancer. In fact, heat and sunlight can transform triclosan into dioxins (Kanetoshi et al. 1987).

Because triclosan is in soaps and other products that are continually flushed down drains, it commonly enters the environment. It has been found at appreciable concentrations in wastewater effluent and surface waters.

Triclosan can also bioaccumulate in fish and amphibians. The antimicrobial can alter how their hormones function, including the thyroid hormone system.

Thyroid hormones play an important role regulating metabolism and during early development in many animals, including humans. Metabolism refers to the way cells use or store energy to maintain life. Food is broken down to create the energy used to grow or maintain tissue. 

The thyroid gland makes and stores thyroid hormones. Spaces in the gland are filled with a substance called colloid. The colloid is rich in the raw materials that are needed to make thyroid hormones. It also serves as a reservoir for the hormones themselves.

Thyroid hormones contain iodine, which can be found in many foods. There are two primary thyroid hormones, thyroxine (T4) and triiodothyronine (T3). Generally speaking, T4 is present at higher concentrations than T3.

In amphibians, thyroid hormones coordinate the metamorphosis of tadpoles into frogs. Laboratory studies find that triclosan interferes with this important transition and has other harmful effects in animals. Metamorphosis was altered in bullfrog tadpoles that were exposed to low concentrations of triclosan. The levels were 15 times lower than what the US Food and Drug Administration has reported in rivers across the United States (Hua et al. 2005).

Low concentrations of triclosan can also alter the genes responsible for producing thyroid hormones (Veldhoen et al. 2006). Other reported effects in fish and amphibians exposed to the antimicrobial include changes in activity level, behavior, sex-ratios, body mass and survivorship (Fraker and Smith 2004).


Newly weaned male rats were fed an oral dose of triclosan of either 0, 3, 30, 100, 200 or 300 mg/kg body weight. The rats were given the triclosan daily for 31 days.

The purpose of the experiment was to determine what effects triclosan would have on concentrations of thyroid hormones and the onset of puberty. Preputial separation (PPS), a separation of the foreskin from the glans penis, was used to measure puberty development.

Researchers measured blood concentrations of testosterone and several other types of hormones and weighed a variety of organs that are essential for rat development and puberty, including the pituitary gland, the testes, the prostate gland and the liver.

Liver enzymes were measured to gauge liver function, and the colloid region of the thyroid gland was examined.

What did they find?

There was a dramatic decrease in the thyroid hormone thyroxine (T4) in rats exposed to increasing concentrations of triclosan. Thyroxine was decreased by 47% at the 30 mg/kg dose and by 81% at the 300 mg/kg dose. There was not a significant difference in thyroxine at the 3 mg/kg dose.

Significant increases in liver weights were seen from the 100 mg/kg to the 300 mg/kg triclosan doses, although certain liver enzymes were not significantly different among groups. The pituitary weights were heavier at the 3 and 300 mg/kg exposure. Other measured organs were not significantly different in weight.

The colloid area of the thyroid gland was smaller in the 300 mg/kg dose group when compared to all other groups.

What does it mean?

Exposure to triclosan dramatically decreased thyroxine concentrations in young male rats. The hormone is critical for normal development and to a properly functioning metabolism. Too much or too little can cause a wide range of health problems before and after birth.

Hypothyroidism occurs when the thyroid produces lower than normal amounts of hormones. The condition can lead to obesity, goiter, infertility, neurological problems and other serious concerns. This long list is not surprising since thyroid hormones control metabolism, which can affect nearly every cell in the body.

The results of this study with mammals support previous research that finds the antimicrobial can affect the thyroid hormone system in animals.

Rats and most other vertebrates, including humans, produce and use thyroid hormones in quite similar ways. Given that triclosan is found in such a variety of household products and has been detected in human blood, urine and even breast milk, this study's findings raises concern for adverse effects on humans. Although this study used rats, the similarities in how the thyroid systems between rats and humans function raises concerns as to whether people could share the same physiological fate.

One thing dissimilar in rats and humans is how much of a compound is necessary to cause a negative result. Sometimes it takes a far greater dose of a chemical to alter a rat's biology than it would to change a human's. Therefore, although the concentrations evaluated in this study were higher than normal human exposure, it is still unclear the concentrations necessary to elicit the same effects in humans. It is possible that the low doses that humans are currently exposed to are enough to cause similar problems.

The colloid area of the thyroid gland was smaller in rats exposed to the 300mg/kg triclosan dose. The colloid is a repository for thyroid hormones and stores components to make more thyroid hormone. A shrunken colloid could indicate that thyroid levels were too low, and the rats were releasing the reserves to bring blood hormone levels back to normal. Using these would reduce the size of the colloid area.

Triclosan exposed rats also had bigger livers. The liver clears and removes toxins from the body. A larger liver may indicate excessive pressure on the liver to clear triclosan. Stressed livers enlarge to accommodate the higher production of the enzymes needed to detoxify substances.

If the liver accelerated its detoxifying activity in the presence of triclosan, the increased effort could account for the lower concentrations of thyroxine measured. The liver would have been clearing the hormone from the system faster. However, the researchers did not find a difference in an important toxin clearing enzyme called UDPGT. This indicates that some other mechanism caused the reduction in thyroid hormones. One way is that triclosan may act directly on the thyroid gland to interfere with hormone production.

There are critical times in development when exposures can permanently alter development. For instance, hypothyroidism during early development can change reproductive tract development, hormone concentrations and sexual maturation, including puberty onset. In this study, triclosan exposure did not change the onset of puberty, suggesting that exposure after weaning to triclosan is too late to affect the timing of puberty

The effects seen in this experiment raise significant questions about the wisdom of allowing widespread use of triclosan in multiple consumer products.


Fraker, SL and GR Smith. 2004. Direct and interactive effects of ecologically relevant concentrations of organic wastewater contaminatns on Rana pipiens tadpoles. Environmental Toxicology 19:250-256.

Hua W, ER Bennett and RJ Letcher, 2005. Triclosan in waste and surface waters from the upper Detroit River by liquid chromatography-electrospray-tandem quadruple mass spectrometry. Environment International 31:621-630.

Kanetoshi, A, H Ogawa, E Katsura and H Kaneshima. 1987. Chlorination of Irgasan DP300 and formation of dioxins from its chlorinated derivatives. Journal of Chromatography 389:139-153.

Singer H, S Muller, C Tixier and L Pillonel. 2002. Triclosan: occurrence and fate of a widely used biocide in the aquatic environment: field measurements in wastewater treatment plants, surface waters, and lake sediments. Environmental Science and Technology 36:4998–5004.

Veldhoen N, RC Skirrow, H Osachoff, H Wigmore, DJ Clapson, MP Gunderson, G Van Aggelen and CC Helbing, 2006. The bactericidal agent triclosan modulates thyroid hormone-associated gene expression and disrupts postembryonic anuran development. Aquatic Toxicology 80:217-227.






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