I have found that a strong cleaner such as "Formula 409" works well, even
after the rash develops.  Spray it on the affected area, and then go ahead
and scratch - scratch - scratch, gently, removing the contaminated skin
surface layer.  From that point on it begins to get better, instead of
continuing to get worse.  Unfortunately this does not work well in extreme
cases where it gets "into your system" and you have rash developing elsewhere
on the body.  Bleach has also been recommended to me.  I have not tried it,
but I strongly suspect it would work too.  Calamine lotion is a waste of time
and money.

Martin