Differential Diagnosis for Small Red Circles on Back

• Single Most Likely Diagnosis
  • Folliculitis: This is an inflammation of the hair follicles, often caused by bacterial or fungal infections. It presents as small, red, and sometimes itchy circles around the hair follicles on the back, making it a common and likely diagnosis for such symptoms.
• Other Likely Diagnoses
  • Contact Dermatitis: An allergic reaction or irritation from substances like soaps, detergents, or plants can cause small red circles on the back. This condition is characterized by redness, itching, and small bumps.
  • Keratosis Pilaris: Although more common on the arms and thighs, keratosis pilaris can appear on the back as small, rough, red bumps due to the buildup of keratin, a protein that protects skin from infections.
  • Pityriasis Rosea: This condition starts with a single large spot (herald patch) followed by an eruption of smaller spots, often on the back, which can resemble small red circles. It's usually accompanied by itching.
• Do Not Miss Diagnoses
  • Lyme Disease: The initial stage of Lyme disease can present with a distinctive "bull's-eye" rash (erythema migrans), which might initially appear as a small red circle. Although not all cases present classically, missing this diagnosis can lead to serious complications.
  • Meningococcemia: This is a severe infection caused by Neisseria meningitidis. It can present with a petechial or purpuric rash (small red or purple spots) that can appear anywhere on the body, including the back. This condition is life-threatening and requires immediate medical attention.
• Rare Diagnoses
  • Erythema Multiforme: A skin condition characterized by target lesions, which can sometimes appear as small red circles. It's often triggered by infections or medications.
  • Sweet Syndrome (Acute Febrile Neutrophilic Dermatosis): Characterized by the sudden onset of fever, leukocytosis, and tender, erythematous, well-demarcated papules and plaques that can appear on the back. It's a rare condition that can be associated with infections, inflammatory bowel disease, or malignancies.