Staphylococcal Scalded Skin Syndrome (SSSS): This condition is caused by staphylococcal toxins that typically affect infants and young children, leading to fever, tachycardia, and a well-circumscribed area of rash that can resemble a burn, with the potential for overlying impetigo due to secondary bacterial infection.

Candidal Diaper Dermatitis with Secondary Bacterial Infection: Candida infections can cause severe diaper rash, and when complicated by a secondary bacterial infection like impetigo, can present with fever and tachycardia.
Bacterial Diaper Dermatitis: Certain bacteria can cause severe diaper dermatitis, which may be complicated by fever and tachycardia, especially if there's an overlying infection like impetigo.

Toxic Epidermal Necrolysis (TEN): Although rare in infants, TEN is a life-threatening condition that can be triggered by medications or infections, leading to widespread skin necrosis and detachment. The initial presentation might resemble a severe diaper rash.
Staphylococcal Toxic Shock Syndrome: This is a severe condition caused by staphylococcal toxins, which can present with fever, tachycardia, and rash, among other symptoms. It's crucial to consider this diagnosis due to its high mortality rate if not promptly treated.

Zinc Deficiency (Acrodermatitis Enteropathica): This rare genetic disorder can cause severe skin lesions, including diaper rash, along with other systemic symptoms like fever and failure to thrive.
Langerhans Cell Histiocytosis: A rare disorder that can cause skin lesions, including those resembling severe diaper rash, along with systemic symptoms like fever and can affect various organs.
Immune-Mediated Disorders (e.g., Chronic Granulomatous Disease): Certain immune deficiencies can predispose to severe, recurrent infections, including those causing diaper rash, and may present with systemic symptoms like fever and tachycardia.