What is the chemical explanation for how a depilatory cream works?  I
am interested in the mechanism, the by products that cause odor, and
the actives that initiate this reaction. - this question is specifice
to people

Hi Sturgie!

Thanks for the question. After quite a bit of research, the answer is
actually rather simple. From a review of a number of dipilatory
creams, the primary ingredients they all have in common are:

Water (carrier)
Mineral Oil (carrier, smooths skin)
Calcium Hydroxide OR Sodium Hydroxide(the active ingredient)
Calcium or Sodium Thioglycolate (also an active ingredient)
A form of alcohol (cetearyl alcohol, isopropyl palmitate, cetyl
alcohol, stearyl ahcohol)
A form of silica
Frangrance

The following website has some interesting facts on depilatory creams.

Hairfacts
http://www.hairfacts.com/methods/shave/jergens.html

"The active ingredient in depilatory creams is calcium hydroxide. The
two compounds act similarly, but sodium hydroxide is much more soluble
in water than calcium hydroxide. The hydroxide ion is a strong base
(alkali), which is why depilatory creams can be so irritating, and why
they break up the hairs."

By the way, the above site also has an excellent forum where you can
ask a question about hair removal and get an answer from an expert.
The forum requires you to register. The moderator quickly answered my
question as a part of this research:

Hairtell Forums
http://www.hairtell.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=8;t=000008

"...depilatories contain a highly alkaline chemical--usually calcium
thioglycolate, calcium hydroxide, or sodium hydroxide--that dissolves
the protein structure of the hair, causing it to separate easily from
the skin surface...A depilatory can cause second- or third-degree
burns, and possibly scarring, if its formula is too strong or if an
inactive ingredient in the product heightens its effect."

I also found the following website with similar information:

Marzena Hair Removal Quick Tips
http://www.depilatory.com/faqs.html#3

"The high pH level in depilatories dissolve the hair at the skin's
surface... While it is completely painless, those with sensitive skin
should patch-test any depilatory in advance."

This page on the same site has some more insight.

Marzen Hair Remaoval Methods
http://www.depilatory.com/recommended.html#depilatories

"The active ingredient (in depilatories), a Thioglycolic Acid,
releases a pungent odor when it is exposed to air, rubbed between the
fingers and/or when it touches the body...However, because the hair is
chemically dissolved at the surface of the skin, the effect is similar
to that of a razor: the hair grows back thicker."

The following site gives a bit more detailed description of the
process.

Wellbeing.com
http://www.wellbeing.com/info_advice_nav/level5.jsp?contentId=1251&level=3#2

"They (depilatory creams) work by penetrating the hair shaft,
dissolving connective tissues and breaking down the cellular material
that glues the dead cells together."

From this and other random research and readings I've done, I can
provide you with the following answer:

Depilatory creams use a strong alkali, or acid, designed to break down
the hair at the cellular level and dissolve it. This same process can
irritate the skin, especially with frequent use. The smells associated
with these creams come from the natural alkali smells associated with
calcium/sodium hydroxide and/or calcium/sodium thioglycolate. There
are no additional odors as a result of the process, from my research.
There are also no major bi-products other than the dissolved hair and
miniscule amounts of vapors caused by the chemical reaction.

It looks as if the answer is not as complicated as I would have first
suspected. But I hope this answers your question. If you need any
additional clarification, please respond with a clarification request,
and I'll see what I can find out.

Thanks for the question! It was fun to research.

Prof

Sodium Hydroxide and Calcium Hydroxide are strong bases (alkalis), not
acids.  Just a note.  Doesn't really matter, unless you were planning
on running chemical reactions with your depilatory cream.

"Bi-products"? Are those products that either men or women can use?

:-)

Hello Sturge
    Depilatory creams/lotions have thioglycolic acid (mercaptoacetic
acid) as the main or active ingredient.This compound belongs
to a group of compounds called the mercaptans.The reaction (hair
removal in this application) is effected by the use of calcium
hydroxide (an alkali).The resulting combination of calcium hydroxide
and thioglycolic acid is calcium thioglycolate(CaTG).The calcium
hydroxide is present in excess to enable the thioglycolic acid to
react with the cystine present in hair protein.The reaction is
2SH-CH2-COOH(thioglycolic acid) +R-S-S-R(cystine)-----> 2R-SH  + COOH
CH2 SS CH2 COOH (dithiodiglycolic acid)
    The dithiodiglycolic acid and R-SH are the byproducts of the
reaction of the depilatory and organic sulphur compounds
  SMELL !.They are also toxic and precautions will have to followed in
handling these type of compounds.
There are also instances where the TG acid decomposes resulting in H2S
as one of the byproducts.Some of the other byproducts
are cyclic sulphur compounds.
 In plain english, the theory of the dehairing action depends upon the
fact that the proteins of hair include a number of cystine
groupings and removal of the cystine sulfide linkages (represented by
the above reaction) destroys the hair fibre and can be easily
washed away.This reaction will  take place in an alkaline medium.   
    I hope this helps . I did check up in Google using calcium
thioglycolate + depilatory and this returned about 150 interesting
 hits .
    I did some work on thioglycolic acid synthesis about 10 years ago
.I wanted a small quantity of TG  to carry out further reactions
 with some other organic compounds ( a devil's brew it was).My
requirements for an assistant was -- a technically qualified person
without a sense of smell !
 Good Luck