Canker Sore vs Cold Sore: How to Differentiate.

Written and reviewed by Slava Fuzayloff | Published on June 1, 2024

Canker sores and cold sores are two common conditions that affect the mouths of people of all ages and genders. Because their appearance inside the mouth is similar, they can be easily confused.

It's important to distinguish between these two conditions because canker sores, unlike herpes, are easily cured and not passed from one person to another.

In this article, we'll talk about the differences between herpes sores (which are sometimes called "cold sores") and canker sores.

When we (doctors) try to differentiate between two medical conditions, we compare two parts of those diseases: history and the visual exam. What does each part mean?

1. History is about:

✓ What caused the rash?

✓ How soon did the rash appear after exposure (the rash incubation period)?

✓ How are the rash and other symptoms changing over time?

2. Visual exam is when we:

✓ Look at the rash

✓ Notice the location of the rash

✓ Pay attention to any discharge from the lesion

✓ Skin depth affected by the lesion

70 % of the diagnosis comes from visual examination, and about 30% comes from history and other associated symptoms and signs. So, the history of the rash plays a confirmatory role.

History

What caused the rash?

Canker sores (also known as aphthous ulcers) are caused by minor trauma, such as biting or eating spicy food. Stress and other factors, such as genetic predisposition, vitamin deficiencies (B12, folic acid, and iron), hormonal shifts (during the menstrual period), toothpaste or mouthwash containing sodium lauryl sulfate, and a weak immune system, can also be potential causes. [4] Canker sore https://www.mayoclinic.org/diseases-conditions/canker-sore/symptoms-causes/syc-20370615

Canker sores are not infectious and cannot be passed from one person to another.

Unlike canker sores, herpes sores are caused by the herpes simplex 1 or 2 virus (usually type 1). Like many infectious diseases, they are transmitted from one person to another by direct skin-to-skin contact. The chance of transmission is about 20% if there are symptoms and 10% without visible symptoms ("silent shedding"). [1] Genital Herpes – CDC Detailed Fact Sheet https://www.cdc.gov/std/herpes/stdfact-herpes-detailed.htm

What is the incubation period, or how soon does the sore appear?

The incubation period is not essential for differentiating herpes from canker sores. It is about the same: 2–4 days for herpes and 1-3 days for canker sore. Both conditions can present as a sore, but unlike herpes skin lesions, which transform to sores eventually (they start as a red skin patch that turns into bumps, blisters, and then sores), chancroid starts as a sore that over time gets bigger and deeper with significant discharge. [2, 4] Genital Herpes Symptoms, Pictures, and Treatment
https://www.webmd.com/genital-herpes/ss/slideshow-genital-herpes
Canker sore
https://www.mayoclinic.org/diseases-conditions/canker-sore/symptoms-causes/syc-20370615

How are symptoms evolving?

What precedes the appearance of a herpes sore and how herpes lesions evolve differentiate herpes from a canker sore

✓ Unlike herpes sores, canker sores are not preceded by systemic symptoms.
Systemic symptoms are fatigue, flu-like symptoms, fever, and swollen lymph nodes.

✓ Unlike canker sores, herpes sores can be preceded by tingling in the area and shooting nerve pain on the side of the lesion. [3] Genital herpes: Overview https://www.ncbi.nlm.nih.gov/books/NBK525769/

✓ A herpes rash goes through multiple stages (skin redness, blister, sore, crusted sore).
A canker sore starts as a sore and stays a sore until it heals.

✓ Canker sores can be on both sides of the mouth.
Herpes sores are clustered on one side of the mouth(left or right) following the skin dermatome and rarely cross the midline.

✓ Both herpes and canker sores heal within a week or two. [3, 6] Genital herpes: Overview
https://www.ncbi.nlm.nih.gov/books/NBK525769/
Canker Sore (Aphthous Ulcer)
https://www.webmd.com/oral-health/canker-sores

✓ Both canker sores and cold sore lesions heal without leaving a scar.

These pictures show the differences between herpes and canker sores.

Visual exam

Where on the body do canker sore vs herpes sore appear?

Canker sores are always inside the mouth, affecting its lining: the gum line, tongue, and throat.

Herpes sores, on the other hand, usually affect the transitional areas of the skin where mucosa meets skin, and they are primarily located outside the mouth.

What do the herpes vs canker sore lesions look like?

A canker sore is a solitary, small oval sore with a red edge and white/yellow center (base). If multiple sores are present, they are usually separated by healthy tissue.

Herpes sores are multiple lesions clustered on the same red base. The base (bottom) of a herpes mouth sore is clear.

How deeply does herpes sore vs. canker sore penetrate the mouth lining?

Unlike herpes sores, which are usually very superficial, canker sores can extend deeper into the soft tissue.

The canker sore can be confirmed by touch- hardness is felt under the base when squeezed. [6] Canker Sore (Aphthous Ulcer)
https://www.webmd.com/oral-health/canker-sores