Simple Definition

Some natural and man-made chemicals can and do interact with the human endocrine system, or are “endocrine active.” In some cases, the interaction between the endocrine system and substances that are endocrine-active is neutral: the substances lack sufficient potency, or exposures may be so low that no effects occur at all. In other cases the body naturally adjusts, and the exposure causes no health effect.

An endocrine disruptor is a natural or man-made substance, external to the body, that evidence shows directly alters the function of the endocrine system, and consequently causes negative health impacts that are confirmed through thorough scientific study.

Advanced Definition

The World Health Organization (WHO) defines an endocrine disrupting chemical as “an exogenous substance or mixture that alters function(s) of the endocrine system and consequently causes adverse health effects in an intact organism, or its progeny, or (sub)populations.”

This internationally accepted definition of an endocrine disruptor has two very important elements: first, that the substance alters the function of the hormonal system, and second, by doing so causes an adverse health effect (i.e. toxicity). The likelihood that an endocrine disruptor will cause harmful effects is based on its potency (how active it is) and potential for exposure (dosage, frequency, and duration).

The definition is important so as not to confuse neutral “endocrine effects” with negative “endocrine disruption,” with the latter term being linked to adverse/negative health effects. Scientists and regulators engaged in screening and testing chemicals for endocrine disruption should use accurate and precise characterizations and refrain from applying labels the imply concern, when that concern is not supported by the evidence.

Regulatory decisions about chemicals that may affect the endocrine system need to be based on several factors—whether a chemical causes endocrine-related activity, how this activity relates to realistic levels and means of exposure, whether negative health impacts have been identified, and what steps can be taken to manage possible risks.

Expanded Definition

An endocrine disruptor is a chemical that alters the function of the endocrine system and consequently causes negative health impacts in an intact organism.

Many things can impact the endocrine system—including stress, food, exercise and exposure to chemicals.

When screening substances for endocrine-related activities, especially when using emerging technologies, regulatory agencies must use validated methods so the results can be relied upon and trusted by all stakeholders.

An indication of endocrine-related activity must be viewed in the appropriate context—it should not be interpreted on its own as evidence of adverse effects.

When conducting safety assessments, regulatory agencies should use a “weight of evidence” approach, meaning all relevant safety data must be considered and regulatory action must not rely simply on one piece of information or a single scientific study.

It is important to distinguish between substances that may interact with the endocrine system from actual endocrine disruptors that can cause adverse health effects. Not every change in the endocrine system will lead to an adverse effect. Similarly, not every substance that interacts with the endocrine system will cause an adverse effect. Certain natural substances, in addition to some synthetic chemicals, can be shown to have the potential to interact with components of the endocrine system while not causing any changes in function of the organism whatsoever; or they may cause transient effects which are readily reversible and do not result in adverse health effects. Therefore, just because a chemical interacts with the endocrine system does not mean it is an endocrine disruptor.

It is important to also note that today’s standardized toxicological tests in laboratory animals already take into account the potential pathways that a chemical could act upon to cause adverse effects, including endocrine pathways. In other words, if a substance causes an adverse health effect via an endocrine pathway (i.e., the substance is an endocrine disruptor), this will typically be revealed through standardized toxicological testing using validated regulatory agency test guidelines.

Through the efforts of governments, academia and industry, considerable progress has been made to develop methods, tests and data that could help answer additional questions about endocrine active and endocrine disrupting chemicals.

There also are safe levels of exposures to substances that have the potential to disrupt the endocrine system, when exposures to such substances are at dose levels and durations that are below the threshold for causing adverse health effects. The presence of a substance that has adverse effects at some level does not imply that the presence of that chemical will lead to adverse effects at all levels. Exposure to trace levels of a chemical – whether it’s a chemical identified as an endocrine disruptor or not – does not necessarily signal impending harm to health. As the Centers for Disease Control and Prevention emphasizes, “The measurement of an environmental chemical in a person’s blood or urine does not by itself mean that the chemical causes disease.”

The Organization for Economic Co-operation and Development (OECD) and the U.S. Environmental Protection Agency (EPA) have developed scientifically-validated screens and tests for identifying chemicals with endocrine active properties to enable science-based examinations of the endocrine disruptor issue. Due to these efforts, regulatory agencies today have access to toxicological screening test guidelines that are relevant, reliable, sensitive, and specific for evaluating the potential for substances to interact with the estrogen, androgen, and thyroid pathways.

Regulatory decisions about chemicals that may affect the endocrine system need to be based on a combination of factors – whether a chemical causes endocrine-related activity; what is the chemical’s potency and levels and means of exposure; whether it produces adverse effects and if so, at what dose levels; and what is the life-stage and susceptibility of an individual.

Regulatory approaches to address the issue of health or environmental concerns for endocrine disruption should incorporate the following steps:

  • Use scientifically valid screening assays and tests for evaluating substances;
  • Implement a rigorous and systematic framework for conducting a weight-of-evidence evaluation that integrates data and information from all relevant and reliable studies;
  • Provide opportunity for stakeholder review and comment and independent peer review; and
  • Use risk-based decision making, taking into account both hazard and potential exposures.

Decisions based on the best science available and on established risk assessment and management procedures will ensure efficient and effective use of limited resources, permit the use of beneficial chemicals, and not unduly alarm the public.