This book started in my shower.
The label on the shampoo had many compounds listed, and due
to my interests in chemistry, most of them were familiar or
had obvious functions. However, one compound stood out as puzzling.
My shampoo listed sodium chloride as an ingredient.
Why was salt in my shampoo?
Since I wasn't likely to be eating it, I doubted it was for seasoning,
despite the strawberry aroma of the liquid. It could have been used
as a preservative, but the remaining ingredients were more likely to
kill microbes than was salt.
Once dry and dressed, I was still curious, so I wrote a letter to the
manufacturer, asking why salt was in my shampoo.
I received a surprisingly enlightening response from the company.
Someone had actually discussed the issue with a chemist, and gave
me an answer that made sense.
The ingredients in the shampoo come from many different manufacturers,
in many different places around the world. From day to day, a particular
batch of shampoo may differ significantly from the previous day in the
amount of moisture brought in with those ingredients.
Salt has the effect of thickening the mixture, and is added to each
batch in the amount needed to raise the viscosity to a specified
level. The customer now gets a product that pours in the same way
each time. This consistency is important to the customer, since
getting a watery product causes suspicions about value, and about
I have told this story many times, sometimes using it to make a point
when teaching chemistry to popular audiences. There are thousands of
chemical compounds in the ingredients lists of products we buy every
day. Knowing what each one is doing in the product has obvious
benefits in comparison-shopping. However, it also provides a sneaky
way of teaching simple chemistry to people who had no idea they would
find it so interesting. I am always looking for ways to make science
more interesting to people who think it is only for people who use
masking tape on their eyeglasses.
The book divides itself into two parts. The first part talks about
common products, and discusses what each ingredient in them does, and
why it is there, or what can be used instead.
The second part is a more in-depth discussion of each compound, usually
accompanied by a structural formula, a picture of the chemical that
allows it to be compared to others. It is in this section that you
will find clearly marked "Chemistry Lessons" occasionally. If I have
done my job properly, these will be interesting, and will relate to
the compound that caught your interest in the first place.
This second part of the book can act as a reference. You can look up
an ingredient you find on a label, and find out more about it. It
may point you to other pages, or other compounds, and you may enjoy
reading the book in this random fashion, rather than front-to-back.
Feel free to do so. Feel free to skip over sections that don't
relate to what you came to find out. The book will be there later,
when you have another question.
This book is not about scaring people. So much of the material you
find on food additives or chemicals in common products is written to
alarm people into changing their behavior in ways that enrich the
writer. They point to the MSDS for a compound, the Material Safety
Data Sheets, that list all of the dire consequences and safety
precautions associated with a compound. These can be quite frightening.
Here is an excerpt from a typical example of an MSDS:
WARNING! CAUSES EYE IRRITATION.
Lab Protective Equip: GOGGLES; LAB COAT
May cause mild irritation to the respiratory tract.
Very large doses can cause vomiting, diarrhea, and prostration.
Dehydration and congestion occur in most internal organs.
Hypertonic solutions can produce violent inflammatory
reactions in the gastrointestinal tract.
May irritate damaged skin; absorption can occur with effects
similar to those via ingestion.
Causes irritation, redness, and pain.
First Aid Measures
Remove to fresh air. Get medical attention for any breathing
If large amounts were swallowed, give water to drink and get
Wash exposed area with soap and water. Get medical advice if
Immediately flush eyes with plenty of water for at least
15 minutes, lifting upper and lower eyelids occasionally.
Get medical attention if irritation persists.
In the event of a fire, wear full protective clothing and
NIOSH-approved self-contained breathing apparatus with full
facepiece operated in the pressure demand or other positive
Ventilate area of leak or spill. Wear appropriate personal
Keep in a tightly closed container, stored in a cool, dry,
ventilated area. Protect against physical damage.
Containers of this material may be hazardous when
empty since they retain product residues (dust, solids);
observe all warnings and precautions listed for the product.
Wear protective gloves and clean body-covering clothing.
Use chemical safety goggles. Maintain eye wash fountain and
quick-drench facilities in work area.
When heated to above 801C (1474F) it emits toxic fumes of
chloride and sodium oxide.
Oral rat LD50: 3000 mg/kg.
Inhalation rat LD50: > 42 gm/m3 /1H.
Skin rabbit LD50: > 10 gm/kg. Investigated as a mutagen,
Label Hazard Warning:
WARNING! CAUSES EYE IRRITATION.
Avoid contact with eyes.
Wash thoroughly after handling.
Label First Aid:
In case of eye contact, immediately flush eyes with plenty of water for at least 15 minutes. Get medical attention if irritation develops or persists.
After reading that, you might expect that such a dangerous chemical
had no business being around people, especially children.
Yet, we can't live without salt. It's even safe enough to put in
What this illustrates is that the MSDS is intended for large
industrial quantities of a substance, not the tiny amounts usually
found in consumer products. Nonetheless, once you are experienced
at reading them, they are a good place to get information on the
safety of chemical compounds. In this book I do not cover safety
issues, except occasionally, and briefly. To do a good job of
that would require a much larger book, and there is already a
wealth of information available.
One should be wary, however, of authors who would advise against
a toothpaste because "it has anti-freeze in it!" The fact that
salt or propylene glycol might make a good anti-freeze is no
reason to ban it as a food additive. Further, creating confusion
between the toxic ethylene glycol, and the food additive propylene
glycol, both of which make good anti-freeze components, is not
doing the consumer any favors.
Fear may help these folks to sell books, or organic toothpaste.
I hope curiosity is the reason you are reading my book.