Dr Kruti Banodkar's, Dermatologist reply to your query -

Hello,

Thanks for posting your query.

From the pictures, I came to a probable diagnosis of
Contact dermatitis
Psoriasis

In my opinion, it is most likely contact dermatitis since you have provided the history that it's not present anywhere else.

The second diagnosis was made keeping in mind the morphology of the lesion and the fact that it's not itchy nor oozing.

I would recommend that you need to apply a prescription strength corticosteroid cream like mometasone on it for ten days. Also application of a moisturizing cream will be helpful.

In case you get similar lesions elsewhere, the diagnosis of psoriasis needs to be kept in mind.

Psoriasis is a condition where the turnover time of the skin is very fast and hence there is accumulation of scales. This condition is not contagious. It can be kept in check with appropriate treatment.

Hope I have answered your query. Please feel free to discuss further.

Take care.