Differential Diagnosis for Small White Pustule on Arm that Hurts when Touched
- Single most likely diagnosis
- Folliculitis: This is an inflammation of the hair follicle, often caused by bacterial infection, which can present as a small, painful pustule. The location on the arm and the pain upon touch are consistent with this diagnosis.
- Other Likely diagnoses
- Pimple or Acne: While more common on the face, pimples can occur anywhere on the body, including the arms, and can be painful if inflamed.
- Ingrown Hair: An ingrown hair can cause a small, painful pustule, especially if it becomes infected.
- Boil or Furuncle: A boil is an infection of the hair follicle that can cause a painful, pus-filled bump, which could initially appear as a small white pustule.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
- Cellulitis: Although less likely to present as a single small pustule, cellulitis is a serious bacterial infection of the skin that can cause pain, redness, and swelling. It requires prompt antibiotic treatment.
- Methicillin-Resistant Staphylococcus aureus (MRSA) Infection: MRSA can cause skin infections that may appear as pustules, and it's crucial to identify and treat them appropriately due to their resistance to many antibiotics.
- Rare diagnoses
- Eczema Herpeticum: A rare but serious complication of atopic dermatitis (eczema) caused by a herpes simplex virus infection, which can lead to widespread, painful vesicles or pustules.
- Kerion: A severe form of tinea capitis (ringworm of the scalp) that can rarely occur on other parts of the body, including the arms, causing painful, pus-filled lesions.