Rigors Underlying Cause
Chills may be caused by:
- When a fever "breaks", the temperature drops, and the patient will often experience chills.
- Bacterial infections:
- More violent shaking chills, known as rigors, can be a sign of an underlying streptococcal infection, such as pneumonia.
- Cold intolerance:
- An abnormal intolerance to cold can be due to hypothyroidism
- Drug side effect
- As the body temperature drops, shaking ensues. This is the body's attempt to raise the core temperature.
- Hot flashes:
- Drug withdrawal:
- Alcohol withdrawal:
PubMed Rigors References
- Batsis JA, Uslan DZ, Baddour LM. 70-year-old man with fever, shaking chills, and weakness. Mayo Clin Proc. 2005 Sep;80(9):1209-12. 
- Call SA, Vollenweider MA, Hornung CA, Simel DL, McKinney WP. Does this patient have influenza? JAMA. 2005 Feb 23;293(8):987-97. 
- Lutfiyya MN, Henley E, Chang LF, Reyburn SW. Diagnosis and treatment of community-acquired pneumonia. Am Fam Physician. 2006 Feb 1;73(3):442-50.