Every day, we apply dozens of different ingredients to our skin, hair, and mouth. Most are harmless, but some have been studied for their potential ability to alter the hormonal system and, specifically, thyroid function. If you want to understand the mechanism—how these substances act on the gland and why it is so sensitive—we explain it in detail in our article on endocrine disruptors and the thyroid.
Here, we get practical: we review the cosmetic ingredients that affect the thyroid or, at the very least, have been linked to it in research. For each one, we tell you what it is, which products it appears in, what it is called in the INCI (the ingredient list on the label), and what is currently known. A warning before we begin: in many cases, the evidence comes from animal studies or association studies in humans, so we are talking about reasonable suspicions, not certainties.
Triclosan
What it is: an antibacterial and preservative agent that for years was added to many hygiene products to give them an "antibacterial" effect.
Where it appears: hand soaps, shower gels, deodorants, toothpastes, and mouthwashes. In the European Union, its use in cosmetics is restricted to specific types of products and maximum concentrations, making it less common today than it was a few years ago, although it can still be found.
What it is called in the INCI: Triclosan. A similar compound, also antibacterial, is Triclocarban.
What is known: it is one of the most studied ingredients in relation to the thyroid. Animal studies have observed that it can reduce thyroxine (T4) levels, and its ability to interfere with the synthesis of thyroid hormones has been studied. In humans, the data is less conclusive, but it is one of the substances most frequently cited when discussing cosmetics and the thyroid.
Parabens
What they are: a family of preservatives widely used for their effectiveness and low cost in preventing the growth of bacteria and fungi in products.
Where they appear: creams, body lotions, shampoos, conditioners, makeup, and wet wipes, among others.
What they are called in the INCI: they end in -paraben: Methylparaben, Ethylparaben, Propylparaben, or Butylparaben. In the EU, some parabens are prohibited in cosmetics, and others have limited concentrations.
What is known: their hormonal activity has been studied primarily in relation to estrogens. Regarding the thyroid, some population studies have found associations between urine paraben levels and changes in thyroid hormones, although results are not always consistent and do not allow for a claim of a cause-effect relationship.
Phthalates
What they are: compounds used to soften plastics and, in cosmetics, primarily as fragrance fixatives and solvents.
Where they appear: perfumes, colognes, air fresheners, hairsprays, nail polishes, and, indirectly, in plastic packaging.
What they are called in the INCI: the most common in cosmetics is Diethyl Phthalate (DEP). Other phthalates, such as Dibutyl Phthalate (DBP) or DEHP, are prohibited in cosmetics in the EU. The problem is that they often do not appear as such, because they can be part of the mixture simply labeled as Parfum or Fragrance.
What is known: several scientific reviews have linked phthalate exposure to alterations in thyroid hormone levels in both adults and during pregnancy and childhood. It has been studied that they may interfere with the transport of these hormones in the blood. Even so, in daily life, we are exposed to phthalates through many routes, not just cosmetics.
Chemical Sunscreens
What they are: molecules that absorb ultraviolet radiation. They are different from mineral filters (zinc oxide and titanium dioxide), which act primarily by reflecting light.
Where they appear: sunscreens, daily creams with SPF, foundation, lip balms, and sometimes in products like shampoos or perfumes to protect the formula itself from light.
What they are called in the INCI:
- Benzophenone-3 or oxybenzone: appears as Benzophenone-3. The EU has reduced the maximum permitted concentrations in cosmetics.
- Octinoxate: appears as Ethylhexyl Methoxycinnamate (sometimes as Octyl Methoxycinnamate).
What is known: these filters have been studied for their hormonal activity. In animal studies, octinoxate and benzophenone-3 have been linked to changes in the thyroid axis, and some studies in humans have found associations between benzophenone-3 and thyroid hormone levels. What you should not do is stop protecting yourself from the sun: if you prefer to avoid them, choose a sunscreen with mineral filters.
Fluoride
What it is: a mineral added to toothpastes and mouthwashes for its effectiveness against cavities.
Where it appears: in most conventional toothpastes, in mouthwashes, and in some dental treatments.
What it is called in the INCI: Sodium Fluoride, Sodium Monofluorophosphate, Stannous Fluoride, or Olaflur (amine fluoride).
What is known: fluoride is not a classic endocrine disruptor, but its potential relationship with thyroid function has been studied, especially in areas with high levels of fluoride in drinking water. With the amounts used correctly in toothpaste, the evidence is limited. If you want to delve deeper, we cover it in our article on fluoride and the thyroid. And if you are considering switching to a fluoride-free toothpaste, discuss it with your dentist first.
Other compounds: perchlorates and heavy metals
There are substances related to the thyroid that you will not see on any label because they are not ingredients, but possible contaminants. Perchlorates, for example, can interfere with iodine uptake by the thyroid, but exposure comes primarily through water and food, not cosmetics. Something similar happens with heavy metals like lead, cadmium, or mercury, which can appear as impurities in some pigments. Here, the only thing you can do as a consumer is choose brands that carefully monitor the quality of their raw materials.
How to identify them on the label
All ingredients in a cosmetic must appear in the INCI, listed from highest to lowest concentration (those below 1% can be in any order). To locate the ones we have just seen, look for the following:
- Look for specific endings and names: -paraben, Triclosan, Triclocarban, Benzophenone-3, Ethylhexyl Methoxycinnamate, Phthalate, or the various Fluoride compounds.
- Be wary of "Parfum" or "Fragrance" without further detail: this is a generic ingredient that can hide dozens of components. Fragrances of natural origin tend to be more transparent.
- Do not rely solely on the front of the packaging: claims like "dermatologically tested" say nothing about these ingredients. The real information is in the INCI.
If you find it difficult to interpret the list, we have a step-by-step guide on how to read an INCI that will help you understand any label in just a few minutes. At Banbu, we formulate without parabens or phthalates and with natural ingredients, so that reading our labels is easy.
If you have hypothyroidism, take care of your skin too
Reducing exposure to these ingredients is a reasonable decision for anyone, but keep in mind that cosmetics do not treat or prevent thyroid diseases. If you have a thyroid disorder, diagnosis, treatment, and monitoring should always be handled by your endocrinologist.
What cosmetics can do is help you take care of your skin and hair, which often suffer when the thyroid functions more slowly. We explain this in our article on hypothyroidism and dry skin, featuring a simple routine for cleansing, hydration, and hair care.
