Understanding Cold Sores and Allergic Reactions

  • Medically reviewed by Emina Ribic (MD) on November 11, 2017. Written by Linda White (MD).

An allergic reaction can lead to cold sores, but there is more to this than meets the eye. In fact, things can become complicated.

While cold sores can form from known allergies, an allergic reaction can also produce blisters of their own. These bumps and rashes typically have no connection to HSV-1. To make matters worse, cold sore treatments can sometimes cause an allergic reaction.

Understanding the basics of HSV-1 can save you a lot of grief when it comes to allergy-related issues. In this guide, you will learn about the symptoms, allergic reactions, and the steps you can take to treat your condition.

What Are the Symptoms of a Cold Sore?

It is essential to define a fever blister. Understanding the symptoms enables you to identify the issue and separate it from skin conditions that are similar to cold sores.

The initial symptom of an outbreak usually involves a slight tingle or even burning sensation on the lip. This will be confined to a single area. This location is typically where the virus (HSV-1) entered your body.

Following the tingle stage, a small cluster of blisters will appear. These blisters will typically increase in size and contain fluid. After a short time, the blisters will burst, and a scab will form.

Once the scab has naturally flaked away, new skin will emerge. At this time the outbreak is considered to be over and the virus no longer contagious. The “typical” outbreak will last no longer than two weeks, (or less) with proper OTC cold sore treatment.

During your initial cold sore outbreak, which is often the most problematic and painful, additional symptoms can also occur. These symptoms include, but are not limited to, fever, headache, mouth pain, and swollen lymph nodes.

To Summarize:

  • Understanding the symptoms and lifecycle of cold sores is critical. This can not only help you to understand HSV-1 and address other ailments. If you find yourself with a blister, yet cold sore symptoms are not occurring, you can likely conclude something else is to blame.[1]

Is It Cold Sores or an Allergic Reaction?

While an allergic reaction can undoubtedly trigger a cold sore, it can also cause other types of blisters.[2] This is why it is so vital to have a basic knowledge of HSV-1 and the symptoms. Not all lip blisters, even for those who carry HSV-1, are cold sores.

Many internal and external elements can trigger a reaction. Some of these elements include the following:

  • Foods
  • Medications
  • Lotions
  • Lip balms
  • Lipsticks
  • Intense weather conditions
  • Existing allergies (ear, nose, and throat issues)

Depending on your unique medical history, allergic reactions are possible. This is especially true if you have a known history and actively attempt to steer clear of specific triggers.

If you have allergies in addition to HSV-1 the water can get a bit muddied.

To recap:

  • Not every lip blister is a cold sore. This even holds true for those who have HSV-1 and have had many cold sore outbreaks. It is entirely possible that your painful blister is related to an allergic reaction.
  • There are several known interactions, both internal and external, that can irritate your lips and mouth. Something as basic as lip balm, for example, could cause lip blisters and irritation if you develop an allergic reaction to its ingredients.
  • Understanding the symptoms of a cold sore can never be understated. This can allow you to define or eliminate the cause of your blisters based on how they have formed and their progress. Knowing the difference between a cold sore and a chemical reaction, for example, can allow you to know what steps (medically) need to be taken.

Allergy due to cold sore meds

Do Cold Sore Creams and Patches Cause Side Effects?

Although quite rare, OTC cold sore treatments can have side effects, just like most any forms of medication.

You are encouraged to stop using your treatment immediately if you begin to notice problematic issues. If your blisters are getting worse with treatment and spreading or swelling you should discontinue use of the product. Should an allergic reaction begin to occur it is conceivable that unrelated HSV-1 blisters could form if the lip and surrounding skin become compromised.

If you have HSV-1 in addition to known allergies, it is important to read the composition of your OTC cream, gel, patch, etc. The last thing you want to do is accidentally inflict harm on yourself due to a chemical or substance that your body is unable to tolerate.

To summarize:

  • As is the case with all forms of medication, it is possible to have an allergic reaction to your OTC meds.
  • You are advised to stop using your treatment selection if your blisters get worse, spread, or lead to any rashes.
  • It is possible that an allergic reaction could impact surrounding skin and introduce blisters that are unrelated to HSV-1.
  • If you are allergic, especially to certain substances, it is important to read the labels. Steer clear of any medications if the composition contains something that you know from previous experience is problematic to your lips and skin.

How to Treat an Allergic Reaction to Cold Sore Medication

If you are experiencing an allergic reaction due to cold sore medication, it is imperative that you consult your physician. Attempting to treat a reaction without a proper diagnosis could make the situation much worse.

Additionally, when consulting your physician, it is essential that you bring your OTC treatment with you. The ability to show your doctor which medication you are taking can be helpful. This will allow the specific issue (reaction) to be identified and hopefully treated in a timely fashion.

Once the adverse reaction has been remedied, your physician will also be able to put you on the right path towards faster cold sore healing. Although rare, some OTC treatments can cause a reaction. It is logical to conclude that some people would have no previous knowledge of any existing allergy before having a cold sore outbreak. This is because cold sore treatments are likely not used for other means.

To recap:

  • The most important thing to do when experiencing an allergic reaction is to consult your physician ASAP. If the symptoms are extreme, an emergency room visit could be in order.
  • If your issues are directly related to a specific treatment, it is important to bring this with you. By presenting medical personnel with the troublesome treatment, the sooner you will likely get relief sooner.
  • Because treatments are not used for other means, it is possible to have a specific allergy and be unaware until your first outbreak. This is especially true if you have naturally sensitive lips and surrounding skin.

How Can You Prevent Allergic Reactions?

The best way to prevent allergic reactions, treatment-related or otherwise, is to identify the cause. While unfortunate, many times it takes a reaction to serve as future avoidance prevention.

Because a potential list of things can cause a reaction, it is important to know your situation. Are you naturally allergic to certain medications? Certain foods? Certain chemicals/ingredients? When it comes to allergies, knowledge is often the best form of prevention. Making notes, quite literally, can often save you from a negative experience in the future.

Most everything can be traced back to understanding HSV-1 and cold sore symptoms. While you might not be able to understand everything fully, you can tell if the problematic blemish is a cold sore or not.

To Summarize:

  • Remembering your bad experiences with specific products, for example, can serve as future prevention. You will only touch a hot stove once. This logic/motto can be applied to various things that have caused you to have a negative reaction in the past.
  • Prevention can be two-fold. It is important to remember that allergic reactions can cause cold sores. While attention has been paid to reaction-causing blisters that are unrelated to HSV-1, reactions can trigger fever blisters. Through acts of prevention, you can kill two birds with one stone. You can quell cold sores as well as other types of blisters caused by outside influences such as food, drink, medication, etc.[3]

The ability to understand HSV-1, as well as your own sensitivities, is critical. You can naturally eliminate many questions from your “worry list” if you are aware of your health.

If you wake up one morning with a blister or rash around your lips, you can likely better access the situation due to your knowledge. By knowing the symptoms, you can probably determine if you have a fever blister or something unrelated. Additionally, if you have known allergies, you might even be able to point to the specific cause.

Is this a cold sore or something else? Just being able to answer that question can lead you on the positive path to proper treatment and healing. If your medication or patch is the cause of the problem, cease treatment and use an alternative without the ingredient that’s responsible.


  1. https://www.dermnetnz.org/topics/blistering-skin-conditions/
  2. Kashyap RR, Kashyap RS. Oral Allergy Syndrome: An Update for Stomatologists. Journal of Allergy. 2015;2015:543928. doi:10.1155/2015/543928.
  3. Scheman A, Cha C, Jacob S, Nedorost S. Food avoidance diets for systemic, lip, and oral contact allergy: an American Contact Alternatives Group article. Dermatitis. 2012;23(6):248–257.

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