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 possible tampering.
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 difficulty.
If large amounts were swallowed, give water to drink and get medical advice.
Wash exposed area with soap and water. Get medical advice if irritation develops.
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 pressure mode.
Ventilate area of leak or spill. Wear appropriate personal protective equipment.
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, reproductive effector.
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 shampoo.
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.
Simon Quellen Field