Infection: This is often the first consideration for chills and flushing due to the body's immune response to pathogens, which can cause vasodilation (leading to flushing) and an increase in the body's temperature set point (leading to chills).

Menopause or Perimenopause: Hot flashes, which can be accompanied by chills, are a common symptom in women undergoing menopause or perimenopause due to hormonal changes.
Anxiety or Panic Attack: These conditions can cause vasodilation and lead to feelings of warmth or flushing, as well as chills due to the body's stress response.
Medication Side Effects: Certain medications, such as antibiotics, hormones, or chemotherapy agents, can cause chills and flushing as side effects.

Septicemia or Sepsis: Although less common, these conditions are life-threatening and can present with chills and flushing due to the systemic inflammatory response to infection.
Malignant Hyperthermia: A rare but life-threatening medical emergency triggered by certain medications used for general anesthesia, characterized by a rapid rise in body temperature, which could initially present with chills and flushing.
Neuroleptic Malignant Syndrome (NMS): A rare, life-threatening disorder caused by an adverse reaction to neuroleptic or antipsychotic drugs, which can present with fever, chills, and changes in mental status.

Carcinoid Syndrome: A rare condition caused by a carcinoid tumor secreting serotonin, which can lead to flushing and other symptoms.
Mastocytosis: A condition characterized by an accumulation of mast cells in one or more organs, which can cause flushing, among other symptoms, due to the release of histamine.
Thyroid Storm: A life-threatening complication of untreated or undertreated hyperthyroidism, which can present with flushing, chills, and other systemic symptoms due to excessive thyroid hormones.