OnabotulinumtoxinA (ONA) is an injectable neurotoxin frequently used to temporarily halt the skin changes associated with aging. Side effects are rare and usually minor, such as bruising, injection site discomfort, and headaches. However, a true hypersensitivity reaction is a serious adverse effect, and clinicians should not attempt another trial if allergy is suspected. We present a case of a benign localized cutaneous reaction following ONA injections in the forehead without signs of an allergic reaction. The rash resolved with topical hydrocortisone, and the patient was able to undergo another trial of injections without recurrence.Alopecia universalis, the complete loss of body hair, during anti-tumor necrosis factor-alpha (TNF-α) biologic therapy is a rare occurrence that has infrequently been reported in the literature. In this case, a 50-year-old man with psoriatic arthritis exhibited alopecia universalis with concomitant onychodystrophy 3 months after initiation with adalimumab. Given the role of TNF-α in the pathogenesis of alopecia areata, it would seem unlikely for anti-TNF-α drugs to induce hair loss; however, it is hypothesized that alopecia areata and its variants may not be dependent on TNF-α and that other factors must be involved. It is important to be aware of such associated adverse effects given that many patients undergo therapy with TNF-α-blocking agents.Seborrheic dermatitis is a common multifactorial skin disorder favoring the scalp, ears, face, and central chest. We present a case of an elderly woman with new-onset severe seborrheic dermatitis with massive facial hyperkeratosis mimicking ichthyosis. Clinicians should be aware of rare presentations of common conditions and should screen for associated medical comorbidities in new-onset severe skin conditions.A 66-year-old man with a recent history of herpes zoster in the second division of the trigeminal nerve presented with hyperkeratotic plaques along his left cheek and temple. A shave biopsy was found to be consistent with postherpetic hyperkeratosis. This case represents a unique presentation of Wolf's postherpetic isotopic response a new skin disorder emerging at the site of a previously healed herpetic, predominantly zoster, infection. We aim to increase awareness of an unusual complication of herpes zoster and the importance of appropriate vaccination to help protect patients from these potential postinfection effects.Hidradenitis suppurativa (HS) is a chronic, recurrent inflammatory skin condition resulting in the formation of nodules, sinus tracts, and abscesses typically in intertriginous regions. HS management is often difficult and involves a multimodal approach, evaluating the benefit of both medical and surgical treatment options, along with treating associated pain and medical comorbidities that present concomitantly with the disease. In this article, we synthesize for the nondermatology clinician the evidence for various HS treatments, along with the diagnostic and therapeutic guidelines for HS published by the British Association of Dermatologists, US and Canadian HS Foundations, HS ALLIANCE, Canadian Dermatology Association, and Brazilian Society of Dermatology. Management of HS requires an individualized, patient-centered approach due to the lack of rigorous evidence for many interventions.Patients with complex chronic disorders, such as asthma, present clinicians with important management problems. The identification of a clinical syndrome usually leads to the diagnosis of the disease entity. The next concern involves classification and a choice as to whether to use a few inclusive categories or multiple exclusive categories. Patients with asthma have multiple clinical syndromes, and these can be described as phenotypes. The use of cluster analysis allows investigators to identify phenotypes with less clinical bias. However, the identification of a particular phenotype does not necessarily provide much insight into the underlying pathogenesis. In asthma, the pathogenetic events are complex and multiple and require a classification based on endotypes. This difficulty introduces the idea of causation and models for causation. Asthma probably does not have a single universal necessary cause. However, it does have multiple sufficient component causes. Understanding these components and their interactions potentially leads to better treatment trials and more focused drug therapy. Clinicians need to identify asthmatic patients and classify them into particular phenotypes; they should also wonder about causation. Clinical investigators need to use these phenotypes to identify more homogenous groups of patients to study the underlying pathogenesis and establish endotypes. Focusing on causation can improve our understanding of disease entities, disease classification, and disease causation. This review outlines ideas relevant to causation in nearly all diseases.Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) or novel coronavirus disease 2019 (COVID-19) emerged from China in December 2019 and progressed to become a global pandemic. Our understanding of its pathophysiology and potential management was initially extrapolated from previous epidemics of coronaviruses like SARS and MERS. SARS-CoV-2 is asymptomatic or minimally symptomatic in more than 80% of patients and requires no additional management; however, the remaining patients progress to pneumonia and hypoxemia with ranging severity, including a smaller group that requires intensive care unit admission. To date, there are no approved treatments for SARS-CoV-2, and current management is focused on supplemental oxygen and supportive care. The antiviral medication remdesivir recently received emergency use authorization by the US Food and Drug Administration for patients with severe disease.  https://www.selleckchem.com/products/hygromycin-b.html  Multiple clinical trials evaluating different treatment modalities such as antivirals, immunomodulators, convalescent plasma, and monoclonal antibodies, among others, are still ongoing. We believe that patients present with clinical phenotypes that correlate with the spectrum of disease. Each phenotype may benefit from one or multiple interventions. We discuss treatments under evaluation in clinical trials and their potential application based on clinical phenotype presentation.