Skin discolouration

[JuneJuly]

Does anyone know what might be causing this discolouration on my dd's(17) skin? It's the same pattern on both forearms, up to mid upper arm. Stops abruptly in a line at the wrist & crooks of elbows are clear. It's also on both sides of her neck, up to the jawline.

Sorry if this is a silly question ! Has she been trying out some fake tan ? Or a moisturiser she didn't realise was tinted for a gradual tan?

I can't see the photo clearly but could it be tinea versicolor?

@mycatallowsmetolivehere - not a silly question! No though, she doesn't use anything like that.

@slashlover - thank you for the suggestion.

After doing some asking around and googling it seems that it's called terra firma-forme dermatosis.

Solution is to clean with 70% isopropyl alcohol to reveal normal skin underneath, as washing with usual cleansers, which is what she'd already tried, doesn't remove it. So we used some hand sanitiser and wet wipes which have worked a treat and her skin is back to normal now.