You work in the coal mines?

Being able to bend backwards is genetic, and at the extremes it's commonly called this:

https://en.m.wikipedia.org/wiki/Hitchhiker%27s_thumb

I haven't heard of your case where you can't bend it forward. Does it hurt or cause any discomfort if you try to move it forward (without help and also with some gentle pressure)?

You should wear gloves at work my friend, that cant be good to absorb through your skin

Straight up, no back bend here, and 90 degree forward at the joint near the nail, the joint near the base does not bend at all. Just genetics.

About 90 degrees for me

My thumb bends towards a brighter future so only slightly

Depends how hard you bend it.

Not like that.

My thumbs used to bend back 90° or more but after years of abusing them and a few injuries, severed tendon here and there, they only bend forwards and straight up now :/

I can't do that with my thumb. Mine goes straight even if I press to force to bend it backwards. It's the only finger joint that doesn't overextend, all my other fingers curve backwards nicely and even more so if I apply pressure.

Bending the thumb forwards (opposite as in your photo) is a different story. The joint can bend past the 90⁰, easily 80⁰ or more if I press it against something.

Same, both thumbs bend backward to 90°. Used to have fun back in school, saying I'd always got my set square with me for geometry.

mine bends about 75° backwards and 90° forwards.

Mine can bend back about 75° back unassisted, nearly 90° assisted. Forward, 90° at the base joint and another 90° at the distal joint.

Nah both are the same and it doesn't hurt.

Applying pressure doesn't move it at all it just locks up

that way

Bout halfway that way. Age stiffens things