The adult intestine hosts a huge number of diverse bacterial species, collectively referred to as the microbiome, that reside mainly in the lower gut, where they maintain a symbiotic relationship with their host. Recent research points to a central role of the microbiome in many biological processes. These microbial communities are influenced by multiple environmental and dietary factors and can modulate immune responses. In addition to local effects on the gastrointestinal tract, the microbiota is associated with effects on other organs and tissues, such as the skin. Indeed, an altered microbiome has been associated with skin disorders in several instances. Thus, in this review, we describe the recent advances regarding the interplay between gut microbiota and the skin. We explore how this potential link affects skin homeostasis and its influence on modulating the cutaneous immune response, focusing on psoriasis disorder. Finally, we discuss how to take advantage of this interplay to manage this disorder, particularly through probiotics administration. In the gastrointestinal tract, the microbiome has been proven to be important in the maintenance of the balance between effector T cells and regulatory T cells, and the induction of immunoglobulin A. Moreover, gut bacterial dysbiosis is associated with chronic inflammatory disorders of the skin, such as psoriasis. Thus, the microbiome can be considered an effective therapeutical target for treating this disorder. Despite some limitations, interventions with probiotics seem promising for the development of a preventive therapy by restoring altered microbiome functionality or as an adjuvant in specific immunotherapy.

Darier disease is a rare type of autosomal dominant genodermatosis, and it is caused by a mutation in the gene coding for the endoplasmic reticulum membrane calcium pump Ca2+-ATPase type 2, leading to compromised intercellular adhesion. Moreover, this condition is characterized by multiple keratotic greasy papules with a seborrheic distribution and is worsened by heat and sun exposure, sweating, and friction. Occasionally, it may be associated with nail abnormalities and may involve the mucosa. Unilateral segmental Darier disease is a rare variant characterized by unilateral eruption of erythematic keratotic papules not associated with other conditions. Herein, we report a case of type 1 segmental Darier disease. Furthermore, the main characteristics and treatment options are discussed.

Tuberculids were originally felt to be related to an allergic response to tubercle bacilli in a patient with tuberculosis at a remote site. They are currently believed to be the result of hematogenous dissemination of organisms from an internal focus to the skin, where they incite a cutaneous inflammatory response. Papulonecrotic tuberculid (PNT) is a form of tuberculids that as the name implies presents clinically as necrotic papules. Herein, we report a case of 59-year-old man who presented with recurrent asymptomatic symmetrical necrotizing papules scattered on his trunk for 9 months. The patient has also crusted plaque on his right forearm. Two skin biopsies were made, one from papulonecrotic lesion on his trunk and the other one from the crusted plaque on his right forearm. The crusted plaque on the forearm showed granulomatous cellular infiltrates and caseation necrosis in the dermis, whereas the papulonecrotic lesions showed patchy perivascular mononuclear cellular infiltrates as well as granulomatous cellular infiltrates in the dermis. Tuberculin test was positive. A diagnosis of lupus vulgaris on the forearm and PNT on the trunk were made based on clinicopathological findings. The patient was seen by chest physician where there was no systemic involvement. Patient was treated successfully with anti-tuberculosis drugs for 9 months with complete resolution of all skin lesions.

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