Uncle Al wrote:
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?

Not necessary unless you are sensitised. The neutral/acid form is
colourless and the alkaline soap form is very water soluble and an
interesting shade of yellow not dissimilar to fluorosene in colour but
without the obvious UV glow. Vegetable acid/base indicator dye.

The smell is also distinctive and I suspect it is a quite bit more toxic
than the fruit - solanaceae are not to be messed with. You can eat
tomatoes and potatoes but the rest of the plant is a really bad idea.
And related species include some extremely toxic plants.

Regards,
Martin Brown