Food allergy testing is frequently requested in atopic dermatitis (AD), yet international guidance appears inconsistent. We performed a structured narrative review of major guidelines, practice parameters, and society statements from North America, Europe, the United Kingdom, and East Asia, current through August 23, 2026. Recommendations were compared by clinical purpose, treatment-response condition, test modality, and intended consequence. The apparent conflict largely reflects three questions being combined: diagnosis of a suspected immediate immunoglobulin E (IgE)-mediated reaction, safe introduction of an allergenic food, and investigation of food as a driver of eczema. Across documents, testing is history-directed and indiscriminate panels are discouraged. For eczema-trigger investigation, NIAID, NICE, Japanese, and Korean guidance uses a treatment-response gate; the AAAAI 2022 work group requires optimal skin care before additional testing, while EuroGuiDerm version 4.0 limits testing for suspected food-triggered eczema to moderate-to-severe disease with a supporting history or suspicion. Prevention guidance differs on pre-introduction peanut screening but agrees on timely introduction. The 2023 Joint Task Force recommendation addresses elimination diets as treatment, not a diagnostic threshold. Positive skin prick testing or food-specific IgE indicates sensitization, not clinical allergy; automatic elimination may cause nutritional harm and loss of oral tolerance. A purpose-first pathway reconciles most apparent conflict and supports clinical confirmation before long-term avoidance.

A 53-year-old man from northeast Mexico presented with acute painful violaceous plaques, hemorrhagic bullae and stellate necrotic eschars on the lower limbs, dorsal hands and external ears. Examination also revealed diffuse non-nodular cutaneous infiltration, madarosis and milphosis, and generalized hypoesthesia-subtle signs of underlying diffuse lepromatous leprosy. IgG anticardiolipin antibodies were positive, raising the possibility of antiphospholipid syndrome. Skin biopsy with Fite-Faraco staining showed endothelial colonization by acid-fast bacilli and polymerase chain reaction (PCR) confirmed Mycobacterium leprae, establishing the diagnosis of Lucio's phenomenon-a rare necrotizing vasculopathy occurring in untreated diffuse lepromatous leprosy. This case illustrates how positive serological mimickers can mislead the workup away from a mycobacterial cause and underscores the need for prompt initiation of multibacillary multidrug once the diagnosis is confirmed.

Dissecting cellulitis of the scalp (DC) and hidradenitis suppurativa (HS) share follicular occlusion, rupture, suppuration, tunnel formation, and scarring, yet are usually classified as separate diseases. Whether DC represents a site-modified scalp phenotype of the same core inflammatory process remains unresolved. To examine the DC-HS boundary and assess whether current evidence favors two distinct diseases or one follicular-occlusion spectrum, we performed a structured PubMed-based critical narrative review through June 25, 2026, evaluating direct comparative evidence and five prespecified domains: clinical morphology, topography, histopathology/pathobiology, follicular-occlusion clustering, and therapeutic response. Direct comparative evidence remains limited. A prospective trichoscopy study identified DC-compatible findings in 8 of 23 men with HS (35%). Across independent domains, however, the convergent pattern is more consistent with a shared core follicular-occlusion pathology whose phenotype may be modified by anatomical site than with two wholly unrelated processes. The current operational definition of scalp HS also creates a diagnostic paradox: an apparently similar scalp phenotype may be labeled scalp HS when intertriginous HS is present, but DC when it is isolated. This supports testing whether extra-scalp HS is a contextual classifier rather than a biological discriminator. We propose DC as a plausible scalp-predominant, site-modified phenotype within the HS/follicular-occlusion spectrum, while emphasizing that molecular equivalence is not yet proven. Resolving this distinction could affect trial eligibility, testing of HS-targeted therapies in DC, reciprocal screening, and outcome-measure development.