The disrupted skin barrier leads to transdermal water loss (leading to the xerosis or dry skin commonly seen in AD) and antigen and allergen penetration of the epidermal layer. Filaggrin mutations are also associated with a decrease in natural antimicrobial peptides found on the skin; subsequently leading to disruption of skin flora and bacterial overgrowth (commonly Staphylococcus aureus overgrowth or colonization).Atopic dermatitis is also associated with the release of pruritogens (molecules that stimulate pruritus or itching) in the skin. Keratinocytes, mast cells, eosinophils and T-cells release pruritogens in the skin; leading to activation of Aδ fibers and Group C nerve fibers in the epidermis and dermis contributing to sensations of pruritus and pain. The pruritogens include the Th2 cytokines IL-4, IL-13, IL-31, histamine, and various neuropeptides. Mechanical stimulation from scratching lesions can also lead to the release of pruritogens contributing to the itch scratch cycle whereby there is increased pruritus or itch after scratching a lesion. Chronic scratching of lesions can cause thickening or lichenification of the skin or prurigo nodularis (generalized nodules that are severely itchy). Diagnosis
AD is typically diagnosed clinically, meaning it is based on signs and symptoms alone, without special testing. Several different criteria developed for research have also been validated to aid in diagnosis. Of these, the UK Diagnostic Criteria, based on the work of Hanifin and Rajka, has been the most widely validated. Treatments
No cure for AD is known, although treatments may reduce the severity and frequency of flares.
Coronavirus diseases are caused by viruses in the coronavirus subfamily, a group of related RNA viruses that cause diseases in mammals and birds. In humans and birds, the group of viruses cause respiratory tract infections that can range from mild to lethal. Mild illnesses in humans include some cases of the common cold (which is also caused by other viruses, predominantly rhinoviruses), while more lethal varieties can cause SARS, MERS and COVID-19. As of 2021, 45 species are registered as coronaviruses, whilst 11 diseases have been identified, as listed below. Coronaviruses are known for their shape resembling a stellar corona, such as that of the Sun visible during a total solar eclipse; corona is derived from the Latin word corōna, meaning garland, wreath, crown. It was coined by Tony Waterson (professor of virology at St Thomas Hospital) in a meeting with his colleagues June Almeida and David Tyrrell, the founding fathers of coronavirus studies, and was first used in a Nature article in 1968, with approval by the International Committee for the Nomenclature of Viruses three years later.The first coronavirus disease was discovered in the late 1920s, however, the most recent common ancestor of coronaviruses is estimated to have existed as recently as 8000 BCE. Human coronaviruses were discovered in the 1960s, through a variety of experiments in the United States and the United Kingdom. A common origin in human coronaviruses is bats. List
See also

Coronaviridae
Alphacoronavirus
Betacoronavirus
Gammacoronavirus
Deltacoronavirus
Novel coronavirus (nCoV)


== References ==