a geometric linear rash

a 16 yo male presented yesterday with a new onset rash.
the rash is diffuse on the whole back, consists of pink-red elevated lines, that are  0.2 cm wide and up to 10 cm lenth. (see picture)
most lines are parallel to the ribs but some of them in 90 degress to the ribs.
there is no pain or itching, fever, arthralgia, new medicine or recent viral infection.
no contact with poson ivy
also he described a different delicate papular rash on his shins and face which dissapeared quickly.
no minor trauma or scraching, and quite reliable.
thank you for your thinking

[maatson]

Bedbug bites ie cimicosis the leisions are linear.

[yudmem]

isn't cimicosis  very pruritic?

[maatson]

Indeed yes, but different individuals express the reaction differently and rarely nonitchy too.My diagnosis was on morphology.Dermographism to what on sat on like old chairs with jute could also elicit a linear response sans itching.

[maatson]

Forgot to add that fictitious dermatitis can present like this too.

[yudmem]

thank you!