+ Balanced, scientifically accurate chemical health information.

Is it safe?

We have all heard the saying “Too much of a good thing.”  This applies to foods, drinks and many kinds of activities.  This saying also applies to chemicals. 

In fact, all chemicals are toxic at some level – but many chemicals have very high levels that won’t cause any harm.  For example, dihydrogen monoxide 1 has many properties that can cause harm to people at high levels, but few folks would want to ban di-hydrogen (H2) mono-oxide (O)---also known as “water”--- from public sale and or other uses.   People usually know that too much water can be harmful, but, of course, water is safe and necessary when we drink a normal amount.

For other chemicals, it’s harder to know what level of chemical is safe. For example, most folks know that arsenic is a poison and that many foods contain small amounts, since it is also part of our environment.  But how much arsenic is safe for people?  You might remember the scare a while back about too much arsenic in apple juice.  The U.S. Food and Drug Administration told us not to worry since the type of arsenic and its level in juice was not harmful.2  

So is the type of the arsenic important too? 

Yes, the type of arsenic and the level a person comes into contact with are both important when we decide if arsenic is safe.  This also applies to other chemicals.

Luckily, many scientists who work for governments, nonprofit groups and other organizations have an important job.  Their job is looking at information about these chemicals to decide the level at which a chemical would cause harm and to determine the level at which the chemical is safe for people.  These safe levels are called by different names by various government organizations, but all of them are found in three steps:

If you want to learn more, government organizations, like the U.S. National Library of Medicine, put a lot of useful toxicity information about chemicals on websites. 4  Nonprofit groups have also been formed to study the safe amount of chemicals and to share information.  Some of these groups, like the Society of Toxicology, have a meeting each year where these organizations from all around the world share their most recent information.5  Other groups, like Toxicology Excellence for Risk Assessment, also study the toxicity of chemicals and post a lot of the information. 6   These are only three examples of many groups that work on chemicals and their safety.

If you want to watch a video about chemical safety, click here.


Michael L. Dourson, Ph.D., DABT, ATS
Board-Certified Toxicologist with the nonprofit organization Toxicology Excellence for Risk Assessment (TERA), dourson@tera.org

Patricia Nance, M. Ed, M.A.
Science Outreach and Initiatives Leader with the nonprofit organization Toxicology Excellence for Risk Assessment (TERA), nance@tera.org


1. See also http://www.dhmo.org/.

2. See also http://www.fda.gov/Food/ResourcesForYou/Consumers/ucm271595.htm.

3. When we are exposed to chemicals at different levels, medical symptoms often occur.   These symptoms include adaptive, compensatory, critical, adverse, and frank or clinical.

When you are exposed to a little too much of the chemical, you will often see something called adaptive effects.  These effects actually improve a person’s chance of not suffering any harmful side effects.   The level of the chemical causing an adaptive effect is usually called the No Observed Adverse Effect Level (NOAEL).  Another idea, called hormesis, meaning that a little bit of poison may be good for you, could also be true here.

As you are exposed to more of the chemical, the person might still stay healthy because their body will show compensatory effects, keeping them safe from the chemical’s harmful effects.  This level of chemical exposures is also usually called a NOAEL. 

When you are exposed to more of the chemical, the critical effect level is reached.  A critical effect is the first harmful effect in a group of people.  For example, let’s say you have a woman and a child in a garage where paint cans are stored improperly.  If the woman feels fine, but the child starts to feel sick, then a critical effect level may have been reached.  Even if the woman is not sick, the child appears to be, and so that level of chemical is the critical effect.  Often, scientists do not have enough information in humans to determine safe levels and then look at data in animals.  The critical effect level is often referred to as the Lowest Observed Adverse Effect Level (LOAEL).   The highest NOAEL below this LOAEL is generally used to determine the safe level.

If we are still exposed to a higher level of chemical, we then have adverse effects.  These effects may show as changes in our body’s chemical makeup, organ function, or physical well-being, like being less able to walk or talk.  Some effects are so severe that a person is unable to move or talk, or an organ may not work at all.  This level of chemical exposure is referred to as a frank effect level.

4. For a listing of safe levels for chemicals from different health organization around the world see http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?iter.

7. See also http://www.tera.org.