Short Answer:
If the sore has not healed within two weeks, or if you are having complications.
Long Answer:
At times when cold sores still exist after two weeks, an infected person is prompted to seek medical advice. A person attacked by cold sores for the first time usually shows severe symptoms. The first attack is often associated with bleeding gums, fever, a lot of agonizing sores, and swollen glands. People often seek medical assistance in order to help ease or lessen the painful suffering of the infected individual. Worse attacks or symptoms often make a person have difficulty in eating and drinking. In this case, a person is more likely to experience dehydration which needs immediate medical attention.
Individuals with a weak immune system are the ones who are most likely to have the worst outbreaks of cold sores. A sever outbreak can trigger various complications and an infected person should acquire medical help. In order to lessen the frequency of the attacks, medical assistance is very important.