My wife and I bought a house. We beleive the previous owners' cats
urinated in the basement, and now our cats our doing the same. My wife
read that hydrogen peroxide can eliminate old cat urine stains/smell.
To her, an indication of success was the foaming reaction it has when
it comes in contact with organic material. However, she has become
alarmed at the same reaction she is getting in many, but not all,
locations in our basement. She is paranoid that there is a large
nascent bacterial population in the basement, and that the foaming of
the hydrogen peroxide, in places a cat couldn't possibly have
urinated; like high shelves; is an indicator. I want to know under
what conditions and with what materials, besides interaction with
bacteria, hydrogen peroxide can foam. For example; wood, pollen,
chemical/cleaner/solvent residue, etc.

Hello there

There are many things that cause hydrogen peroxide to react (foam). 
If bacteria were the main cause, then it would foam on our skin, and
it doesn't.  It will foam on a cut in the skin however.

While many people use it as an antiseptic, it is not very good at that
job.  It is good for washing cuts and is better than no antiseptic at
all. - - "The reason why it foams is because blood and cells contain
an enzyme called catalase. Since a cut or scrape contains both blood
and damaged cells, there is lots of catalase floating around...When
the catalase comes in contact with hydrogen peroxide, it turns the
hydrogen peroxide (H2O2) into water (H2O) and oxygen gas (O2)."

There is no catalase on uncut skin therefor no reaction, bacteria
present or not - and we already know there is a lot of bacteria on
even the cleanest skin.  No peroxide reaction just from the presence
of bacteria.

So the statement - - "She is paranoid that there is a large nascent
bacterial population in the basement, and that the foaming of
the hydrogen peroxide, in places a cat couldn't possibly have
urinated; like high shelves; is an indicator." - - such an indicator
is in fact not correct.  Hydrogen peroxide whether foaming or not is
not an indicator of the presence or absence of bacteria.  It is only
an indicator as to whether reactants of some kind are present.

Another of these reactants which may cause her peroxide to foam is
detergent.  If the shelves have been washed in the past, then residual
detergent could cause the foaming reaction.  In fact the reaction of
hydrogen peroxide and detergent is the basis for many school science
projects.
As in this 'kids' page of interesting things to do with science:
http://www.coolscience.org/CoolScience/KidScientists/h2o2.htm   - add
food coloring and you will have colored foam.

This reaction with residual detergents could explain why some parts of
the basement show reactions and others don't.

As stated at the beginning, hydrogen peroxide reacts with many things.

It oxidizes hydrogen sulfide, mercaptans, amines and aldehydes. -
Destroys residual chlorine and reduced sulfur compounds thiosulfates,
sulfites, and sulfides)  Oxidizes cyanides, NOx/SOx, nitrites,
hydrazine, carbonyl sulfide, and other reduced sulfur compounds
mentioned above.  Organic oxidation - Hydrolyzes formaldehyde, carbon
disulfide, carbohydrates, organophosphorus and nitrogen compounds, and
various water-soluble polymers; and (with catalysis) destroys phenols,
BTEX pesticides, solvents, plasticizers, chelants, and virtually any
other organic requiring treatment.  Oxidizes ferrous iron, manganese,
arsenic, and selenium.

List of reactive substances found above is gathered from Introduction
to Hydrogen Peroxide - Application Overview
http://www.h2o2.com/intro/overview.html

If fact, hydrogen peroxide reacts with so many things that a simple
layer of dust on the shelf may contain one or more reactive substances
thus causing the foam.

The one thing it does not react with in a manner which would be
visible, is bacteria though that does not mean that bacteria are not
present along with the material the peroxide does react with.

Since you are dealing with a house instead of a chemical lab, my first
bet would be a reaction to residual detergent from previous efforts at
cleaning.  It takes very little detergent to set off the foam.

And as for the cat urinating on high shelves, perhaps indirectly. 
Microscopic crystals from dried urine can go a-blowin' in the wind and
may settle as dust many places in sufficient quantity to cause a
reaction in the most unlikely spots.

I hope the last three paragraphs set your wife's mind at ease.

Search - google
Terms - hydrogen peroxide reactions, hydrogen peroxide uses

If I may clarify anything before rating the answer, please ask.

Cheers
Digsalot

I have a PhD in chemistry and I sometimes amuse myself by looking at
GA, particularly this section.  Over the past few months, I've noticed
a disturbing trend: answers are getting more and more incorrect,
sometimes downright the opposite of reality.  I would advise you to be
very careful and use GA answers to science questions with some
caution.  Some GA researchers have no business answering chemistry
questions: if you've gotten an F in high school chemistry, don't try
to become a chemist in 20 min.
This particular answer is a good example.  H2O2 will not react with
soap or most detergents.  Decomposition of H2O2 (especially very
dilute solutions that are available to public) would reqire a very
potent catalyst, such as a transition metal ion.  Granted, microbes
alone would probably not decompose H2O2 fast enough to see it.  A more
likely explanation is that the shelves have been treated with a metal
salt, stained perhaps.  I would throw away such shelves, you don't
know what's in them; besides, staining materials w/ metal salts is
19th century technology.  In general, if H2O2 foamed, I would be
concerned.

Thanks acrh2.  Anything that can make an answer clearer is welcome. 
However, getting a reaction from hydrogen peroxide (3% in store
solution) and detergent is an old and established elementary school
science demonstration.

See the link I posted.

Cheers
Digs

Back to the link I posted.  It seems yeast is needed in the equation.

Perhaps you are right.  Archaeologists should not answer chemistry
questions. But between us we may have things covered.

Thanks again for the input.  By the way, I did get A's in highschool
chemistry.  Trying to remember 40+ years ago.

digs

Perhaps, I spoke too harshly, and I'd like to appologize.  Don't feel
bad though, as even for a simple molecule such as H2O2, its chemistry
can be extermely complicated and rich.  When I mentioned this question
to my supervisor, who happens to be a world class expert on H2O2
chemistry, she wouldn't give a simple answer.  In my own experience,
H2O2 reactivity strongly depends on its partner, for example, aqueous
Fe(III) ions will decompose H2O2 very slowly, while catalase, whose
active center also features a heme bound Fe(III) ion, is one of the
fastest natural calasysts.  I am not sure of the composition of feline
blood, especially in its dried form, but it's quite possible that it
might do the job.  The best way would be to do an experiment, but you
could also check for high Fe, Mn, Cu content, which would be
necessary.  It is also possible that some detergents might contain
high transition metal ion concetrations, especially iron.  Wood stains
is another possibility.
Remember though, there's no single general answer that would cover every situatuion.

And one more thing that I just saw.  "Foaming reaction" maybe be a
very poor indication that things are getting desinfected.  Foam
production in itself is just an indication of H2O2 decomposition, 2
H2O2 -> 2H2O + O2, which has nothing to do w/ desinfecting things,
because the active oxygen in H2O2, used for oxidizing/desinfecting,
ends up as molecular oxygen O2 without doing its job.