Q. What causes blisters on the lip?

Answered by
Dr. Dilip Meena
and medically reviewed by Dr.Nithila A
This is a premium question & answer published on Apr 20, 2019

Hello doctor,

Last week I woke up with what appeared to be three to four tiny blisters on my upper left lip, outside of the mouth, not inside. I recently had a baby and have not left the house except to go to a dental appointment one week before developing these small blisters. I went to the doctor a few hours after finding the blisters, and she ran an Ig blood test which came back negative. I also had an HSV 1 and HSV 2 test done before seven months before giving birth that came back negative. So I know I was not a carrier of the virus.

After seeing what could be the beginning of primary infection, my doctor prophylactically put me on a dose of Valtrex. Three days before we did a culture swab test which came back today as negative. My question is, are there any possible ailments that would closely mirror a cold sore?

I understand that if my primary infection was only two weeks ago, it is possible that it would be undetectable in the bloodstream but I was surprised that the culture swab came back negative as well. Could this be because of the use of Abreva earlier in the day? The blisters never leaked much fluid, so it was quite hard to get a great sample on the swab.

After a few days, the blisters never turned into an open sore, just slowly dried and tingled a little. At this point, they appear to be gone entirely. There was never any pain associated with the sore.



Welcome to icliniq.com.

1. There can be other skin diseases which mimic HSV 1 infection on lips, but still, it is quite characteristic clinically, things which can sometimes look like are paederus dermatitis, hand foot, and mouth disease, but it is seen usually in children and blisters elsewhere are also present. Candida can be there, but it rarely presents as blisters in adults.

2. To conclude the appearance is quite characteristic and your description of vesicles and their evolution looks like HSV.

3. The serology can take up to a month (average 2 to 4 weeks) to become positive after primary infection, HSV IgM will be detectable at that time in serum. So it might be one of the reasons for that.

4. For culture the sensitivity overall is 50 percent, that is 50 out 100 patients culture will grow the virus. Although in primary syphilis sensitivity is up to 80 percent.

5. When lesions start to heal it is difficult for a culture to get a positive result. Also, fluid will be required for it to be positive. Either fluid from blisters or erosions whatever is present. It will not come positive if the sample is taken from the surface of the vesicle.

6. My advice is to repeat serology after 3 to 4 weeks once again, and even if it is positive, you do not need to get frightened so much as HSV 1 serology is usually seen in 50 to 75 percent cases. It does not mean it will come back again, though being a carrier chance of spread is there somewhat.

Thank you doctor,

I do have one more question regarding transmission. I have a child and an infant as well as my husband. I understood that asymptomatic shedding occurs so do I live life as if I always have a cold sore? If so, it will definitely change the nature of all of our relationships.

Is kissing my baby possible? Can I intimate with my spouse without protection even while not showing signs of a cold sore?



Welcome to icliniq.com.

1. Yes, you are right that asymptomatic shedding occurs and it remains there in different severity indefinitely.

2. Chances of transmitting it to others are high during the active episode via direct contact such as kissing or oral sex although it can spread during the asymptomatic period as well, chances are less.

3. As the time pass by the opportunity of spread during the asymptomatic period also reduces but remains there.

4. As it is not possible to give antivirals life long for the minimal risk of transmission always remains indefinitely, there are no guidelines for this anywhere in the world.

5. In short, you can take precaution during the active episode only to avoid direct mucosal contact.

6. As I told you earlier, it is widespread in the general population. Data suggest that about 3.5 billion people worldwide have HSV and no one recommend avoiding mucosal contact even in the asymptomatic period.

7. No treatment is required in asymptomatic period unless you are having multiple episodes (more than six in a year) yourself, then one need to give daily Acyclovir which is known as suppressive therapy. I hope it helps.

Thank you doctor,

You have offered so much more information than I had been given before. Thank you for your time and expertise.



Welcome back to icliniq.com.

You are most welcome. I am glad that you found all the information useful. Have a great time ahead. Take care.

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