What is on my hand after gardening?

[PingaPenguin]

Slightly strange question I know.

Mowed the lawn then went round pulling out longer grass/weeds from the edge. Not long after felt a funny tickly/tingly feeling on my thumb. Look at my hand a little later and it's covered in this white stuff. What is it from?

[FauxFox]

Does it wash off? Surely it's just plant sap?

[traviata]

Do you think it's an allergic reaction? Euphorbia is often a culprit, although it wouldn't usually be a weed at the edge of the lawn.