On Sat, 16 Jan 1999, Hagerty, Marjorie A. wrote:

> Foolishly, I picked up a bottle of 30% H202 to check an expiration date
> without gloves on. Must have been some dried solution on the outside
> because my hands burned and turned white. Does anyone know why your
> hands turn white and then it goes away in a few hours.

  I have had exactly the same experience, usually accompanied by
  multiple tiny pinprick sensations, which precede the whitening.
  The discomfort and the colour change are stopped by immediate
  rinsing in water.

  Hydrogen peroxide bleaches melanin, the pigment in hair and skin,
  and concentrations of 1 to 3% are used to make peroxide-blonde
  hair. The 30% solution is altogether fiercer. It can't dry on the
  surface of the bottle (H2O2 is a liquid, which evaporates at
  much the same rate as water). Probably some droplets of the liquid
  escaped from the vented bottle-cap and floated through the air
  onto your hands. The bottle is vented because H2O2 decomposes in
  the presence of traces of impurities, yielding oxygen and water.
  This could cause dangerously hight pressure in a tightly capped
  container.

  I think the reason for the quite rapid disappearance of the
  bleached areas is that the offending droplets of H2O2 are very
  small and affect only one or two layers of the keratinized dead
  cells of the stratum corneum of the epidermis. This is enough
  to increase the amount of reflected light, but the cells are
  soon desquamated.

  The instability of 30% H2O2 is a pain in the neck. You never know
  if your stock solution is OK until you get a negative result with
  a peroxidase stain. It's tempting to use a tuberculin or insulin
  syringe + needle to withdraw the 0.1 ml or so needed to make up
  a peroxidase incubation medium. I can attest to the fact that
  doing this kills a whole 500 ml bottle of 30% H2O2. A week later
  it's just water. Checking the bigger chemistry books tells why:
  the decomposition of hydrogen peroxide is catalyzed by many metals,
  and also by many other commonly encountered substances. It's sensible
  to buy small volumes, but 100 ml costs nearly as much as 500 ml.

  You can avoid these difficulties by using UREA HYDROGEN PEROXIDE
  (UHP) instead of 30% H2O2. Urea hydrogen peroxide is a white solid.
  It contains H2O2 molecules trapped in cages of urea molecules. It is
  very soluble in water, yielding a solution containing hydrogen
  peroxide and urea (which doesn't seem to interfere in any way with
  peroxidase histochemistry). The solid material is treated as
  35% H2O2. It's convenient to weigh out about 0.2 grams and dissolve
  it in enough water to make about 50 ml of 1% H2O2. This is good for
  a month in a really clean glass bottle. If you can't or won't clean
  bottles thoroughly, you can make up a new 1% solution every day.
  The stuff is quite cheap ($20 for 100g) as lab chemical go. The label
  tells you to keep the solid at 4C, which I have done. It would be
  interesting to find out if the fridge is really necessary. My stock
  is about 6 years old, and still in good working order.

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1