Allergic Contact Dermatitis

I've had a rash on both wrists for almost two months now. At first, it started as clusters or red bumps/pimples. Eventually, the initial intensity subsided. However, while some red bumps would heal and disappear, new ones would continue to form in the area -- though nowhere near asa many as were present initially. I also get a few bumps on my thumb, nowhere near the main rash on my wrists. Also, there was never any pain or itching.

A biopsy suggested that the rash is consistent with allergic contact dermatitis; however, it seems highly unlikely that I've been re-exposing my hands to the same allergen for the past two months. None of my products changed, and I went on vacation during the middle of the course of the rash (so difft environment, clothes, food, etc), and the fact that it's only on my wrists mainly (where I wear nothing) also calls into question whether I'm repeatedly engaging with an allergen. I've also been on strong topical corticosteroid creams, to no avail. Now, I'm about to being treatment with oral prednisone.

Meanwhile, I'm wondering, if this is, indeed, allergic contact dermatitis, is it possible that I exposed my hands to an allergen two months ago and my body continues to react (by producing antibodies, I guess) seven weeks later? (I'm attaching a photo of the rash on one hand -- but do note that it looks particularly inflamed due to a recent biopsy in the area.) Does anyone have any thoughts on this?