Repeating Rifle wrote:

This morning, I spent a fair amount of time clearing out excess growth of
tomatoes in my little greenhouse. When I washed my hands, they turned very
yellow. That had happened before but I did not know what the cause was. I
thought that I had contacted nitrates from my nutrient solution and that it
had somehow caused the yellow color the same way that exposure to nitrate
does. I presumed that the alkaline soap was the proximate cause for turning
a leuco compound yellow.

This time, after washing away the color, I went back out and handled the
tomato plants some more. Hand washing brought out the yellow color again.

Is this typical of tomatoes? What is the substance involved?

Sounds like lycopene from the tomatoes or another carotenoid from the
foliage. Mild oxidation will then remove the color (benzoyl peroxide
acne cream; Oxy-Clean, dilute bleach), as will electrophiles (skunk
juice). Why don't you wear gloves?

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf