There is no so-called “fastest” way to reduce a baby’s fever of 40 degrees, and the most common methods of reducing fever include taking antipyretic drugs and physical therapy. 1. antipyretic drugs: commonly used antipyretic drugs include ibuprofen, acetaminophen, in general, more than three months of the baby preferred acetaminophen, more than six months of the child these two drugs can be used. 2. Physical therapy: Physical cooling methods include applying antipyretic patches, warm water wipes, drinking more water, etc. You can use 32-34 ℃ warm water baths, warm water wipes the parts of the child’s neck, groin, armpits, etc.; clothes should not be worn too thick, or else it is not conducive to heat dissipation. The baby high fever of 40 degrees need timely medical treatment, you can do the first heat treatment on the way to the hospital, wait until the hospital and then according to the doctor’s guidance for the next step in the treatment.