My girlfriend found different colored hairs in my shower drain. She
doesn't beleive me that they are probably hers, and that the hair
changed color over time after it sat in the drain for a while. What
causes dark hair to turn light in a shower drain?

Thank you.

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Clarification of Question by bniz-ga on 22 Feb 2006 07:56 PST

BTW - It's not bleach, as I've never used it before.

Bleach.

It's famous for lightening hair and it's also sometimes used as a
domestic disinfectant (sometimes hiding under trade names).

Get a bottle QUICK!

I have a friend, Jemima, who,
Mistook Domestos for shampoo.
Her hair's much cleaner than before;
A shame it's lying on the floor.
 
http://www.mud.co.uk/richard/dobleach.htm

The chemical name to look out for is sodium hypochlorite (household bleach).

There are a couple of possible scenarios that could lead to what you're saying.  
1) If you really aren't using any bleach, other household cleaners may
may a bleaching or lightening effect on the hair simply becuase they
can dissolve the pigment in the hair, while the keratin body of the
hair remains strong.

2) Soap may do the same thing, if it remains in contact with the hair
long enough, as soap is almost always basic (pH >7) and as such is a
mild caustic and dessicant (both of which would break apart the
pigments in the hair).  In addition, anything with a peroxide in it
(such as acne treatments, face washes, etc) will lighten hair.

The problem with the answer that the hair is being lightened by
something you're putting down the drain is that all the hair in the
drain would be lightened, not just a strand.

3)So what probably happened is that your girlfriend is actually
looking at her own hair, largely unadulterated.  Many people don't
realize it, but you have hairs of all different colors in your head. 
Even individual strands have different colors within themselves. 
Also, hair is shinier when it is wet (and coming out of your shower
drain, it was probably wet), and so it can look lighter when viewed
one strand at a time.  Finally, hair can become encrusted with various
soap residues, proteins from your body, and various other forms of
dirt when it sits in your shower drain.  These usually look gray or
white, so it could be that there is just some filth on the hair that
is making it look the wrong color.

Or, maybe your girlfriend is the one with the other girlfriend, and
this is just a sly cover.

If the hair has roots on, like if its been pulled out when shampooing
etc. then you can get a DNA test. DIfficult, expensive way but its
always an option!!!

Whatever you do, DON'T have the hairs DNA tested.

Just buy a bottle of household bleach, pour half away; take the
remains to  the G/F; and innocently enquire if 'this stuff' might
possibly have caused it.

Good Luck!

Check with your municipality to find out if Chlorine is used to treat
your water supply. Chlorine can lighten hair.