Doxycycline applied in early pregnancy may affect fetal bone growth and lead to fetal malformations. Doxycycline is a tetracycline, a kind of antibiotic, which can be used for the treatment of many kinds of pathogen infections, such as Rickettsia, Mycoplasma, Chlamydia and so on. Animal experiments have shown that the drug can cross the placenta and can impede bone growth, affecting fetal development and possibly leading to fetal malformations. The use of tetracyclines during the period of dental development, such as late pregnancy, infancy, childhood, etc., may lead to permanent tooth discoloration. Pregnant women, children and other people need to avoid the use of tetracyclines as much as possible, and those who are allergic to the drug are also prohibited from using it, and need to consult a doctor before using the drug.