Stealth Chemicals: A Talk by Dr. Shanna Swan of the Children’s Environmental Health Center

On Earth Day, 2014, Dr. Shanna Swan of the Children’s Environmental Health Center at the Icahn School of Medicine at Mt. Sinai came to Sprout’s NYC store to discuss stealth chemicals: what they are and where we can find them. We took notes!

What Are Stealth Chemicals?

For over 50 years we have all been subjected to a covert experiment without our consent. We are exposed to hundreds of man-made chemicals through our food, our water and in products we use in our daily lives.  Swan calls these “stealth chemicals”; they enter our bodies silently, without our knowledge (“under the radar”), bypassing our body’s defense systems, and causing long-term harmful effects.

During the past 50 years, there have been alarming trends in human health; increases in rates of obesity and diabetes, asthma, and neurobehavioral problems in children (including autism and ADHD) as well as decreases in sperm count and fertility.  Could these health problems be related to our silent exposure to these stealth chemicals?  Swan believes the answer is “Yes”.

The Creation of Synthetic Estrogen

In the 1930’s while looking for a chemical that could mimic natural estrogen, a British chemist (Charles Dodds) hit the jackpot when he synthesized diethylstilbestrol (DES). It was cheap, unpatented, and was soon prescribed worldwide for a variety of reasons including for use in pregnancy to prevent miscarriage. Since the children exposed prenatally seemed healthy at birth, it was presumed to be safe. But DES-exposed daughters were found to have cancer in their reproductive organs over twenty years later. (Read more about that in our article, Daughters of DES: A Cautionary Tale.)

From this experience we learned that the placenta does NOT protect the fetus, that:

  1. a chemical can impact the development of the fetus and,
  2. it can produce devastating consequences years after the birth of an apparently healthy child.

BPA Started as a Synthetic Estrogen

Even before Charles Dodds created DES, he had discovered another synthetic estrogen, bisphenol A (BPA). DES was more potent and became the widely used pharmaceutical, while BPA was found to strengthen plastics and is still widely used in plastics today. And even in plastics, it has hormonal effects. Science is showing that BPA, even at very low doses, can alter many aspects of development.

Endocrine Disruptors

And these dangers are not limited to synthetic estrogens. Estrogen is only one of many hormones made by our bodies. Many chemicals used in everyday products can alter our hormones. These are termed Endocrine Disruptors. Small children are particularly vulnerable to these chemicals; they are rapidly growing and are too young to have developed the protective mechanisms they will have as adults. (Read more in our article The Endocrine System & the Harms of Endocrine Disruptors.)

Scientific Research into Endocrine Disruptors

Since researchers aren’t allowed to administer these chemicals to people, they must use lab animals to learn about their risks. Animals have shown us that very small changes in hormone levels can cause profound alterations in normal development.

In utero, a mouse gets hormones from his mother, makes some himself, AND he gets some from his neighbors. The sex of his neighbors influences his development. When he is located between two males, he gets just a little more testosterone. How much more? Less than 1 part per trillion. (1 part per billion is 1 drop in an Olympic-size pool, 1 part per trillion is 1000 times smaller than that!) And this small amount of testosterone can alter the size of his genitals and even his fertility as an adult. Extremely small changes in testosterone at critical periods can cause significant changes in development.

At conception the sex organs are “undifferentiated”, and female genitals are the “default”. Early in pregnancy the production of testosterone sets the stage for the development of the male genitals. For this all to happen normally, the male must “see” sufficient testosterone at the right time during gestation. Endocrine disruptors can reduce this testosterone peak and thus the size and function of male genitals.


Phthalates are one large class of endocrine disrupting chemicals. Phthalates are found everywhere; in our food, our homes (in polyvinyl chloride – PVC), in cosmetics and because they make plastic soft and flexible, in children’s toys. Phthalates can lower the body’s natural levels of testosterone.

Phthalates enter our bodies without our knowledge when we eat foods and drink beverages and breathe air containing them. And they can even enter intravenously (like in the newborn nursery).  Then our body breaks them down, and we can measure those breakdown products—called metabolites—in our urine.

Phthalates are petroleum-based, high production chemicals.

Two Phthalates of Particular Concern

First, there is DEHP, the most potent phthalate that has been studied. It makes plastic products soft and flexible and so it is used widely throughout our homes and our hospitals. Babies in the intensive care nursery get large doses of DEHP. The major source of DEHP exposure (as well as other phthalates and BPA) for most of us is our food. Plastics are used in food processing, shipping, and storageDEHP significantly decreases testosterone in the male fetus.  

DBP is also of great concern. It is in our cosmetics, perfumes, paints and lacquers. We inhale DBP, and it enters our bodies through our skin. It also lowers testosterone. 99% of the US population has measurable levels of this and other phthalates, and if you were pregnant, this would tell you what your fetus was being exposed to.

In rodents, prenatal exposure to these phthalates results in a cluster of changes to the genital tract that alters the animals’ fertility when they mature. The cluster is called the “phthalate syndrome” and it includes the anogenital distance (AGD). AGD is an easy way to distinguish newborn males from females in mice; it is about twice as long in males as females.

“Phthalate Syndrome” in Humans

In 1999 Swan decided to see whether she could see a “phthalate syndrome” in human infants. She recruited pregnant women and stored their mid-pregnancy urine sample. To look at the phthalate question, they contacted these mothers and invited them to bring their children in for a physical exam, an exam designed to identify the specific changes that make up the phthalate syndrome. After measuring phthalates in the mothers’ urines she saw that, as hypothesized, and as seen in rodents, the higher the phthalate levels (particularly DEHP and DBP), the shorter the boys’ AGD.

And there were other differences in boys whose mothers had higher DEHP metabolites: they had smaller penises; their testicles were more likely to be incompletely descended.

Will this matter as the boy grows up? In animals, the answer is “yes”. Rodents with smaller AGD and other markers of the phthalate syndrome have smaller testicles and less sperm as adults. And our new data in young men suggests that the same may be happening in humans.


Testosterone is important for the development of other systems in the body.  For example, just as adequate testosterone is needed for proper development of a boy’s reproductive tract, it is needed for proper brain development. Parts of the brain that depend on testosterone can influence how young animals (and children) play. Male animals exposed to chemicals that lower testosterone during development play in a way that is less male-typical than expected.

The bottom line is that male reproductive function has been declining for the past 50 years. The number of sperm in men from industrialized countries is now half what it was 50 years ago. And during this time there have been comparable declines in men’s testosterone levels and significant increases in testicular cancer. And endocrine disrupting chemicals like the phthalates have now been widely recognized as an important source of this increasing problem.

The Good News

These chemicals are non-persistent. Unlike dioxin and DDT, which stay in our bodies for decades, phthalates and BPA are gone from our bodies in hours or days. So, if the sources were eliminated, exposure would rapidly decrease.

Stealth Chemicals in our Marketplace

There are over 80,000 chemicals in commerce. The vast majority of these chemicals, and thousands of “stealth chemicals”, have undergone no testing to evaluate their risk to human health.

Our current exposure to huge numbers of untested chemicals should not continue. There are safer alternatives (many being identified by green chemistry) and we have choices. It should not be up to the consumer and the parent to make those choices.

As we’re waiting for legislation to catch up, Sprout San Francisco offers a fully vetted selection of products that are free from toxic chemicals, including the stealth chemicals.