Drug Reaction: This is often the most common cause of a rash accompanied by eosinophilia. Many drugs can induce an allergic reaction, leading to skin manifestations and an increase in eosinophil count. The reaction can range from mild to severe, including conditions like Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS).

Atopic Dermatitis (Eczema): A chronic condition characterized by itchy, inflamed skin. Eosinophilia can be present, especially during acute flare-ups.
Insect Bite Reactions: Reactions to insect bites can cause a rash and may lead to eosinophilia, especially if there is a significant allergic response.
Parasitic Infections: Certain parasitic infections, such as hookworm or roundworm infestations, can cause eosinophilia along with skin manifestations.
Allergic Contact Dermatitis: An allergic reaction to substances that come into contact with the skin, which can lead to a rash and sometimes eosinophilia.

DRESS Syndrome (Drug Reaction with Eosinophilia and Systemic Symptoms): A severe drug reaction that can be life-threatening. It presents with a rash, fever, lymphadenopathy, and internal organ involvement, along with eosinophilia.
Eosinophilic Leukemia: A rare condition but critical to diagnose early. It can present with eosinophilia and various systemic symptoms, including skin manifestations.
Hypereosinophilic Syndrome (HES): A group of disorders characterized by the overproduction of eosinophils, leading to organ damage. Skin manifestations can be part of the presentation.

Eosinophilic Pustular Folliculitis: A rare skin condition characterized by recurring itchy, pus-filled bumps, often associated with eosinophilia.
Well's Syndrome (Eosinophilic Cellulitis): A rare condition presenting with cellulitis-like symptoms and significant eosinophilia.
Churg-Strauss Syndrome (Eosinophilic Granulomatosis with Polyangiitis): A form of vasculitis that can present with asthma, eosinophilia, and various systemic symptoms, including skin manifestations.