Many chemicals, both natural and man-made, may mimic or interfere with the body’s hormones, known as the endocrine system. Called endocrine disruptors, these chemicals are linked with developmental, reproductive, brain, immune, and other problems.

Endocrine disruptors are found in many everyday products, including some plastic bottles and containers, liners of metal food cans, detergents, flame retardants, food, toys, cosmetics, and pesticides.

Some endocrine-disrupting chemicals are slow to break-down in the environment. That characteristic makes them potentially hazardous over time.

Endocrine disrupting chemicals cause adverse effects in animals. But limited scientific information exists on potential health problems in humans. Because people are typically exposed to multiple endocrine disruptors at the same time, assessing public health effects is difficult.

What are some common endocrine disruptors?

• Bisphenol A (BPA) — used to make polycarbonate plastics and epoxy resins, which are found in many plastic products including food storage containers
• Dioxins — produced as a byproduct in herbicide production and paper bleaching, they are also released into the environment during waste burning and wildfires
• Perchlorate — a by-product of aerospace, weapon, and pharmaceutical industries found in drinking water and fireworks
• Perfluoroalkyl and Polyfluoroalkyl Substances (PFAS) — used widely in industrial applications, such as firefighting foams and non-stick pan, paper, and textile coatings
• Phthalates — used to make plastics more flexible, they are also found in some food packaging, cosmetics, children’s toys, and medical devices
• Phytoestrogens — naturally occurring substances in plants that have hormone-like activity, such as genistein and daidzein that are in soy products, like tofu or soy milk
• Polybrominated diphenyl ethers (PBDE) — used to make flame retardants for household products such as furniture foam and carpets
• Polychlorinated biphenyls (PCB) — used to make electrical equipment like transformers, and in hydraulic fluids, heat transfer fluids, lubricants, and plasticizers
• Triclosan — may be found in some anti-microbial and personal care products, like liquid body wash

How do people encounter endocrine-disrupting chemicals?

People may be exposed to endocrine disruptors through food and beverages consumed, pesticides applied, and cosmetics used. In essence, your contact with these chemicals may occur through diet, air, skin, and water.

Even low doses of endocrine-disrupting chemicals may be unsafe. The body’s normal endocrine functioning involves very small changes in hormone levels, yet we know even these small changes can cause significant developmental and biological effects. This observation leads scientists to think that endocrine-disrupting chemical exposures, even at low amounts, can alter the body’s sensitive systems and lead to health problems.

When absorbed in the body, an endocrine disruptor can decrease or increase normal hormone levels (left), mimic the body's natural hormones (middle), or alter the natural production of hormones (right).

Endocrine systems, also referred to as hormone systems, are found in all mammals, birds, fish, and many other types of living organisms. They are made up of:

• Glands located throughout the body;
• Hormones that are made by the glands and released into the bloodstream or the fluid surrounding cells; and
• Receptors in various organs and tissues that recognize and respond to the hormones.

Hormones act as chemical messengers that are released into the blood stream to act on an organ in another part of the body. Although hormones reach all parts of the body, only target cells with compatible receptors are equipped to respond. Over 50 hormones have been identified in humans and other vertebrates.

Hormones control or regulate many biological processes and are often produced in exceptionally low amounts within the body. Examples of such processes include:

• blood sugar control (insulin);
• differentiation, growth, and function of reproductive organs (testosterone (T) and estradiol); and
• body growth and energy production (growth hormone and thyroid hormone).

Much like a lock and key, many hormones act by binding to receptors that are produced within cells. When a hormone binds to a receptor, the receptor carries out the hormone's instructions, either by altering the cell's existing proteins or turning on genes that will build a new protein. The hormone-receptor complex switches on or switches off specific biological processes in cells, tissues, and organs.

Some examples of hormones include:

• Estrogens are the group of hormones responsible for female sexual development. They are produced primarily by the ovaries and in small amounts by the adrenal glands.
• Androgens are responsible for male sex characteristics. Testosterone, the sex hormone produced by the testicles, is an androgen.
• The thyroid gland secretes two main hormones, thyroxine and triiodothyronine, into the bloodstream. These thyroid hormones stimulate all the cells in the body and control biological processes such as growth, reproduction, development, and metabolism.

The endocrine system, made up of all the body's different hormones, regulates all biological processes in the body from conception through adulthood and into old age, including the development of the brain and nervous system, the growth and function of the reproductive system, as well as the metabolism and blood sugar levels. The female ovaries, male testes, and pituitary, thyroid, and adrenal glands are major constituents of the endocrine system.

Hypothalamus - The hypothalamus links our endocrine and nervous systems together. The hypothalamus drives the endocrine system.

Pituitary gland - The pituitary gland receives signals from the hypothalamus. This gland has two lobes, the posterior and anterior lobes. The posterior lobe secretes hormones that are made by the hypothalamus. The anterior lobe produces its own hormones, several of which act on other endocrine glands.

Thyroid gland - The thyroid gland is critical to the healthy development and maturation of vertebrates and regulates metabolism.

Adrenal glands - The adrenal gland is made up of two glands: the cortex and medulla. These glands produce hormones in response to stress and regulate blood pressure, glucose metabolism, and the body's salt and water balance.

Pancreas - The pancreas is responsible for producing glucagon and insulin. Both hormones help regulate the concentration of glucose (sugar) in the blood.

Gonads - The male reproductive gonads, or testes, and female reproductive gonads, or ovaries, produce steroids that affect growth and development and also regulate reproductive cycles and behaviors. The major categories of gonadal steroids are androgens, estrogens, and progestins, all of which are found in both males and females but at different levels.

In the last two decades there has been a growing awareness of the possible adverse effects in humans and wildlife from exposure to chemicals that can interfere with the endocrine system. These effects can include:

• developmental malformations,
• interference with reproduction,
• increased cancer risk; and
• disturbances in the immune and nervous system function.

Clear evidence exists that some chemicals cause these effects in wildlife, but limited evidence exists for the potential of chemicals to cause these effects in humans at environmental exposure levels. Very few chemicals have been tested for their potential to interfere with the endocrine system. Current standard test methods do not provide adequate data to identify potential endocrine disruptors (EDs) or to assess their risks to humans and wildlife.

In recent years, some scientists have proposed that chemicals might inadvertently be disrupting the endocrine system of humans and wildlife. A variety of chemicals have been found to disrupt the endocrine systems of animals in laboratory studies, and there is strong evidence that chemical exposure has been associated with adverse developmental and reproductive effects on fish and wildlife in particular locations. The relationship of human diseases of the endocrine system and exposure to environmental contaminants, however, is poorly understood and scientifically controversial (Kavlock et al., 1996, EPA, 1997).

Disruption of the endocrine system can occur in various ways. Some chemicals mimic a natural hormone, fooling the body into over-responding to the stimulus (e.g., a growth hormone that results in increased muscle mass), or responding at inappropriate times (e.g., producing insulin when it is not needed). Other endocrine disruptors block the effects of a hormone from certain receptors (e.g. growth hormones required for normal development). Still others directly stimulate or inhibit the endocrine system and cause overproduction or underproduction of hormones (e.g. an over or underactive thyroid).

Certain drugs are used to intentionally cause some of these effects, such as birth control pills. In many situations involving environmental chemicals, however, an endocrine effect is not desirable.

One example of the devastating consequences of the exposure of developing animals, including humans, to endocrine disruptors is the case of the potent drug diethylstilbestrol (DES), a synthetic estrogen. Prior to its ban in the early 1970's, doctors mistakenly prescribed DES to as many as five million pregnant women to block spontaneous abortion and promote fetal growth. It was discovered after the children went through puberty that DES affected the development of the reproductive system and caused vaginal cancer.

Since then, Congress has improved the evaluation and regulation process of drugs and other chemicals. The statutory requirement to establish an endocrine disruptor screening program is a highly significant step.

Growing scientific evidence shows that humans, domestic animals, and fish and wildlife species have exhibited adverse health consequences from exposure to environmental chemicals that interact with the endocrine system. To date, such problems have been detected in domestic or wildlife species with relatively high exposure to:

• organochlorine compounds (e.g., 1,1,1- trichloro-2,2-bis(p-chlorophenyl);
• ethane (DDT) and its metabolite dichorodiphenyldichloroethylene (DDE);
• polychlorinated biphenyls (PCBs), and dioxins); and
• some naturally occurring plant estrogens.

​Effects from exposure to low levels of endocrine disruptors has been observed as well (e.g., parts per trillion levels of tributyl tin have caused masculinization of female marine molluscs such as the dog whelk and ivory shell). Adverse effects have been reported for humans exposed to relatively high concentrations of certain contaminants. However, whether such effects are occurring in the human population at large at concentrations present in the ambient environment, drinking water, and food remains unclear.

Several conflicting reports have been published concerning declines in the quality and quantity of sperm production in humans over the last 4 decades, and there are reported increases in certain cancers (e.g., breast, prostate, testicular). Such effects may have an endocrine-related basis, which has led to speculation about the possibility that these endocrine effects may have environmental causes. However, considerable scientific uncertainty remains regarding the actual causes of such effects.

Nevertheless, there is little doubt that small disturbances in endocrine function, particularly during certain highly sensitive stages of the life cycle (e.g., development, pregnancy, lactation) can lead to profound and lasting effects (Kavlock et al., 1996. EPA, 1997)

Our understanding of risk factors for reproductive problems such as infertility, low birth weight, prematurity, fetal and infant death has increased over the past decades. Certain health conditions, social and economic factors, and behaviors can increase the risk of adverse reproductive and birth outcomes. We have also learned that environmental exposures can play a role in reproductive and birth outcomes. However, thereis still much we do not know.

Exposure and Risk

The following are some of the possible environmental exposure and risk factors that are associated with reproductiveand birth outcomes:

• Exposure of nonsmoking pregnant women to environmental tobacco smoke (also known as second hand smoke) may be a risk factor for preterm birth, low birth weight, and possibly fetal death or miscarriage.
• Exposure to air pollution may be related to both low birth weight and preterm birth, even at low levels.
• A pregnant woman's exposure to lead may cause preterm birth, low birth weight, and spontaneous fetal death or miscarriage.
• Exposure to pesticides has been associated with fetal death (miscarriage) and babies being born too small, but more research is needed in this area.
• Although age and certain health conditions are more commonly associated with infertility, it is believed that environmental contaminants may cause infertility by creating other health conditions. For example, some research suggests that environmental contaminants can affect a woman's menstruation and ovulation. Low-level exposures to compounds such as lead and pesticides are suspected risk factors for women. Exposure to compounds such as lead and polychlorinated biphenyls (PCBs) have been linked to decreased sperm quality among men. Much more research needs to be done to find out how environmental contaminants may be affecting human fertility.
• Some scientists have suggested that environmental hazards can affect how many males are born. Parents and the fetus can be exposed to different hazards referred to as endocrine disruptors. Fewer males are conceived when exposure to endocrine disruptors causes a decrease in testosterone. Diethylstilbestrol (DES), a synthetic estrogen widely prescribed to pregnant women during the mid-1900s, is a strong endocrine disruptor. Previous studies have suggested an association between endocrine-disrupting compounds and the secondary sex ratio (the sex ratio of the grandchildren of the exposed women). Several studies show that declines in the sex ratio of males to females at birth may be associated with occupational exposure, or exposure to air pollution.

Prevention

Women who are pregnant or may become pregnant should follow their doctor's advice on how they can have a healthy baby. Doctors can also answer questions on fertility and give advice on conceiving. Early and regular prenatal care helps identify conditions and behaviors that can result in adverse reproductive and birth outcomes.

Here are some ways to prevent environmental exposures:

• Stop smoking and avoid secondhand smoke.
• Limit outdoor activity when the Air Quality Index shows unhealthy levels of air pollutants.
• Cut out or reduce any indoor sources of particulate matter, like wood-burning stoves and fireplaces, and try to reduce the amount of time spent outdoors near areas with higher levels of air pollution, such as areas with a lot of traffic.
• Stay away from lead.
• Stay away from mercury. Some fish, especially albacore tuna, may have been contaminated with mercury. State health departments sendout public fish consumption guidelines that pregnant women can follow.
• Do not use pesticides if you are pregnant. Stay away from rooms that have been recently sprayed with insecticides and from other areas with potential pesticide exposure.

Take a look around your home. Do you know what’s in your household goods and products? Some chemicals can harm your health if too much gets into your body. Becoming aware of potentially harmful substances and clearing them out can help keep you and your family healthy.

“There’s a range of chemicals that you can be exposed to in your home, generally at very low levels,” says Dr. Andrew Rooney, a toxicology and risk expert at NIH. Possible toxic substances can be found in building materials, cookware, cleaning products, shower curtains, furniture, carpet, and other common items.

Not all chemicals are harmful. In fact, most substances in our environment are likely safe, explains Dr. Heather Patisaul, a neuroscience and toxicology expert at North Carolina State University. “Only a small subset is probably toxic,” she says. “Although that’s worrisome, there are many simple things you can do to help minimize your exposure.”

Often, it’s how much you’re exposed to that can make a chemical harmful. The amount that’s “safe” varies for each substance. NIH-funded researchers are working to learn more about how chemicals in the environment can affect our health, so we can better address any issues.

Sometimes it’s obvious when a chemical is hazardous. You may get a rash from spilling a household cleaner on your skin. Or you may start coughing when you breathe in irritating fumes. To avoid known health risks, be sure to read the instructions carefully on your household products, and follow any safety precautions.

Some toxic chemicals cause no immediate or clear symptoms. Lead, for example, is well known for its poisonous effects. Generally, the more lead you have in your body, the more likely you’ll have health problems. Lead can cause high blood pressure, fertility problems, muscle and joint pain, and memory and concentration problems. As a result, lead is no longer allowed in paints, gasoline, and cans used for food. But lead can still be found in lead-based paint used in older homes, household dust, and drinking water pumped through leaded pipes.

“The best way to protect yourself from the health effects of lead is not by treatment but rather by preventing exposure,” Rooney explains. If you live in an older home, check with your local health department about any lead that may be in the paint, dust, or drinking water. Local experts can guide you in steps you can take to prevent lead exposure.

Young children are more vulnerable to lead and many other chemicals. That’s because their bodies and brains are still developing. Kids can also be exposed to toxins from normal childhood behaviors, like playing on the floor and putting their toys or hands in their mouths.

“Chemicals can come out of our products and end up in the air and dust in the home, where they can enter your body,” says Dr. Ami Zota, an environmental and public health expert at George Washington University. Her team recently discovered 45 different chemicals that are commonly found in indoor dust. Many of the identified chemicals belong to a group called “endocrine disruptors.”

When endocrine disruptors get into your body, they can mimic or block the natural hormones your body makes. Evidence suggests that endocrine disrupters might reduce fertility, raise the risk for some cancers, or cause other harms. These chemicals may pose their greatest health risks when people are exposed in the womb or during their first few years of life, when hormones are guiding development of the body’s organs and brain.

Substances thought to cause endocrine disruption include certain fragrances, pesticides, and stain-resistant coatings. NIH-funded researchers study the health effects of several types of chemical classes tied to hormone disruption, including phthalates (pronounced THAL-ates), PFCs (or perfluorinated chemicals), and flame retardants.

Phthalates are a family of man-made chemicals used to make plastics, cleaners, and fragrances. The human health effects of phthalates are not yet fully known but are being studied by several government agencies, including NIH. In animals, phthalate exposure has been linked to many reproductive health and developmental problems. To reduce your exposure, read product labels and avoid using products that contain phthalates. Some—but not all—phthalate-containing products might be clearly labeled: “contains phthalates.” But sometimes phthalates might be listed as a 3- or 4-letter abbreviation, such as BBP, DBP, or DEP. These phthalates must be listed among the ingredients on product labels, unless they are added as a part of the “fragrance.”

“Many hundreds of chemicals can be classified as fragrance,” Patisaul explains. “So when you use a cleaner with a scent, it probably has some phthalates in it—even though the label doesn’t specifically say phthalates.” You can look for “fragrance-free” products. The U.S. Environmental Protection Agency (EPA) also provides the “Safer Choice” label, which is used on products made with ingredients that are safer for human health and the environment.

PFCs are widely used to make everyday products more resistant to stains, grease, and water. They can be found in nonstick cookware, stain-resistant sofas and carpets, and waterproofed clothing and mattresses. In animal studies, some PFCs disrupt normal hormone activity, reduce immune system function, or cause developmental problems. Some evidence suggests that certain PFCs may also affect human health, with possible ties to low birth weight, obesity, and testicular and kidney cancers.

Certain PFCs, like those used to make Teflon, are being phased out of use in the U.S. But some older household items, like nonstick pans, may still contain them. If you have an older nonstick pan that is dinged and worn out, try to replace it.

Flame retardants are added or applied to materials to slow or prevent a fire. But a growing body of evidence links many of these chemicals to negative health effects in animals and humans. Flame retardants can be found in foam, upholstery, mattresses, carpets, curtains, and fabric blinds. Flame retardant use has been declining in recent years. But these chemicals are still found in some products. When buying new items, especially for children, try to purchase furnishings filled with cotton, polyester, or wool, instead of polyurethane foam.

“The best thing is to become aware that there are chemicals in your environment, and there are very simple things that you can do to lower your exposure,” Patisaul says.

Chemicals are everywhere, and most are harmless. Limiting the potentially toxic ones in your day-to-day life can help you create a safer, healthier home.

Learn what’s in the products you purchase, and make informed decisions. You can also take steps to get rid of risky chemicals by keeping the dust down in your house. See the Wise Choices box for some useful tips.

Keep Indoor Spaces Healthy

To reduce potentially toxic substances in your home:

• Clean with “Safer Choice” or non-toxic products.
• Dust using a damp rag.
• Use a wet mop to clean floors.
• Vacuum with a high-efficiency particulate air (HEPA) filter.
• Open a window or use a fan to improve air circulation when you’re cleaning.
• Have and maintain a good ventilation system in your home.
• Wash your hands and your children’s hands often.