Another gluten-related condition
Dermatitis herpetiformis is an itchy, blistering skin disease that also stems from gluten intolerance. The rash usually occurs on the elbows, knees and buttocks. Dermatitis herpetiformis can cause significant intestinal damage identical to that of celiac disease. However, it may not produce noticeable digestive symptoms. This disease is treated with a gluten-free diet, in addition to medication to control the rash.  
Mayo Clinic - Celiac Disease

Dermatitis herpetiformis is the most well known skin disease associated with celiac disease.  In fact, if there is a positive skin biopsy for DH, a celiac disease diagnosis is accepted. However, not all with DH will show damage on intestinal biopsy.

Because DH is so well documented elsewhere, I don't feel the need to include much on this page. 

There are almost 3000 references on Pubmed, including almost 300 full text articles available.

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Dermatitis herpetiformis (DH) is characterized by chronic, itching papules, seropapules, small vesicles and, exceptionally, large blisters. The distribution of these polymorphic symptoms around the elbow, knee, buttock, and back is suggestive of the diagnosis. DH is further confirmed by the accumulation of granulocytes at the papillary dermis, resulting in a subepidermal split formation and by the presence of a unique, granular IgA precipitate in the uppermost dermis. Prognosis is predominantly determined by other autoimmune pathologies, malabsorption, or very rarely by lymphomas. Some of these diseases can be prevented by an early-onset, strict gluten-free diet, which is therefore the suggested treatment option.
An exception within the group of autoimmune blistering diseases: dermatitis herpetiformis, the gluten-sensitive dermopathy.
PMID:22560138  May 2012