Lactational mastitis is a common condition during breastfeeding, which, in rare cases, can progress to life-threatening necrotising mastitis, particularly in cases where Streptococcus pyogenes is involved. The development of streptococcal toxic shock syndrome (STSS) is associated with a fatality rate of approximately 50%. In this Grand Round, we present the case of a healthy mother, aged 35 years, breastfeeding a child diagnosed with scarlet fever. The mother subsequently developed lactational mastitis, with a high load of S pyogenes, culminating in skin necrosis and STSS. This case, along with six more case reports identified in a thorough literature search, underscores the severity of lactational S pyogenes mastitis. In all cases, the only identifiable risk factor for invasive S pyogenes disease was close contact to individuals exhibiting symptoms of scarlet fever. During breastfeeding, the direct contact of the nipple to the child’s pharynx, containing S pyogenes in the case of scarlet fever, presents a probable route of transmission, especially when considering the pathogenicity of the bacterium. Although breastfeeding is generally encouraged, the current literature lacks sufficient guidance regarding breastfeeding practices in children with scarlet fever. This Grand Round proposes a simple strategy to minimise maternal risks, offering valuable insights into clinical management and prevention.