When is the temperature a concern on a newborn? When should I take him to the dr?

Any over 100.4 F. Newborns are supposed to be well protected from most viruses by getting plenty of immune factors from mom.Any temperature over 100.4 (rectal) in the newborn or first 6-8 weeks is worrisome for a bacteria that may have been acquired at birth. I generally admit & treat all with IV antibiotics until it's clear they don't have a bacterial infection.This is why we advise against lots of people contact.
Depends on how old. . 28 days and under - 38c or 100.4f. 29-56d - 38.2c or 100.8f. Take the baby to the doc if they hit those temps or look sick or you're just worried.