I've been struggling with rash(es) for two years and have seen 2 docs. The first one refused to even look at the rash (she literally would not let me take my shirt off to show her) and diagnosed it as dermatitis. The second one diagnosed Grover's based on a biopsy. The Grover's has gradually subsided, knock on wood, but the rash – in my mind it's all related but looks different in areas of different types of skin – has been excruciatingly itchy in my armpits and most recently in my inner elbows, to the point of waking me from sleep. The doc never gave me a name for it, but it looks exactly like the photos of atopic dermatitis that I've seen (thanks to @gardeningjunkie for helping to identify it) – an extremely itchy, inflamed redness in tender areas including neck, armpits, and inner elbows, especially streaking in the creases and, when it gets worse, erupting into bumps and even sores, looking a little like poison ivy. The only thing my doc's offered that's helped is prescription cortisone cream, which is thinning the skin to the point that I'm afraid to keep using it; but when I stop, the rash quickly worsens. (Even extra-strength over-the-counter cortisone does not noticeably help.)
I did have a comprehensive patch test, which turned up very slight allergies to a substances I don't use much if ever. I've been using non-allergenic soaps and laundry detergents for many months without noticing any improvement.
Sarna never did a thing for me. I do have a moisturizer I like called Epiceram – I'm not clear whether it's prescription, but my doc prescribed it and it comes from the pharmacy – but it does nothing for the itch. I've been cleaning my skin thoroughly at least once per day using a mixture of 2/3 witch hazel and 1/3 alcohol, which provides temporary relief from the itching but does dry the skin out, and then applying prescription cortisone and/or a non-greasy moisturizer such as Epiceram (rightly or wrongly, I gave up moisturizers with any oil in them during my initial struggles with Grover's, since I read that demodex are a suspected factor, and they feed on sebum, and it did seem to me that some of the oily things I tried made it worse). I've also been experimenting with adapalene gel, hoping it would help with healing and strengthen the thinning skin; not sure if it's doing anything.
Fwiw, I developed asthma around the same time the rash(es) started, and other members of my family have had eczema or other skin conditions I know less about.
As for diet, I can second gardeningjunkie's observation that a substantial subset of people in Mayo's Grover's forum say it's helped them greatly. So far it has not been convenient for me to do the cilantro smoothie they recommend for Grover's, but I have been taking Metal Magic, which is made from cilantro and chlorella, and it's possible that that is why the Grover's has been better lately. Apart from that, at present, my own diet consists almost entirely of whole grains, low-fat dairy (which I love and which I hope might help with my osteoporosis), fruit, nuts, and veggies – pretty healthy, but not exactly a strict anti-inflammation diet as I understand it.
I would love to hear what others struggling with atopic dermatitis have experienced, especially if they've found anything that helps.