Thank you very much for this interesting question. Usually, when one
hears "no tears shampoo" the first thing that comes to mind is
JOHNSON'SŪ NO MORE TEARSŪ Baby Shampoo so I searched their website.
Here's what I found on their FAQs page:
"I received an email that said the reason why JOHNSON'SŪ Baby Shampoo
was gentle to the eyes was because it contains numbing agents that
numbs the eyes if contact occurs."
"The assertion that chemicals are added that numb the baby's eyes is
totally false. The reason JOHNSON'SŪ shampoo formulas do not irritate
the eyes is the mildness of the formulation, which has undergone
extensive clinical testing and has proven to be as gentle to the eyes
as pure water."
(Source: Johnson & Johnson FAQs [ http://www.johnsonsbaby.com/faq#23
], Johnson & Johnson Consumer Companies Inc., Copyright 1998-2004.)
Personally, I don't believe that there's a numbing agent mixed in "no
tears" shampoo. These products have been around for years and there's
no clear epidemiological evidence to support that claim.
So what makes it tearless?
"Shampoo is used to cleanse the hair. The primary ingredient of a
shampoo is a detergent. Many shampoos, particularly those targeted for
babies and children, claim to cause non eye irritation or sting. A
"no-tear" formulation achieves this claim by carefully adjusting the
nature of the detergents. In particularly, the identity and
concentration of detergents with anionic or "charged" portion are
controlled to minimise both eye and skin irritation."
(Source: What makes a no-tears shampoo? -
C.C.C. Heep Woh College Chemistry Department, Copyright 2003)
From the info above, the quick answer to your question is: "no tears"
shampoo works because the detergents and other chemical irritants are
formulated to a certain level that minimize eye irritation.
But take note...
"There is no such thing as a tearless shampoo. Even straight water
poured into the eyes will cause enough irritation to produce tears. A
product can be made friendlier to the eyes by using gentler
surfactants, but it is still not tearless!"
(Source: Leave-in products and grooming -
http://www.duurstede.ca/articles.html, Duurstede Grooming Products,
The W. R. Van Wyck Group Limited, Đ April 4th, 2004)
There's a video that discusses this topic in more detail in case you're interested:
Inquiring Minds: Episodes: 15 & 16 - BPN 6322H
"No Tears Shampoo"
61 programs x 5-8 minutes (2 programs per tape). For pricing please
inquire at: firstname.lastname@example.org
"what makes" "no tears" shampoo
"what makes" "tearless shampoo"
"how do" tearless shampoo work
I hope this helps you. If you have a question, please feel free to
post your clarificationand I'll attend to you as soon as possible.
Thanks for asking.