A temperature of 100.4°F (38°C) is often considered a low-grade fever in adults. This slight elevation in body temperature can indicate that the body is fighting an infection or illness. Normal body temperature typically ranges from 97°F to 98.6°F (36.1°C to 37°C), so a reading above this range may warrant attention. In children, a temperature of 100.4°F can also signal a fever, which may be caused by various factors, including viruses, bacterial infections, or even teething. Monitoring the fever and accompanying symptoms is essential for determining if medical intervention is necessary.