What causes Herpes Simplex Labialis (HSL), also known as cold sores, on the lips?

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Last updated: February 25, 2025View editorial policy

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From the Guidelines

Herpes Simplex Labialis (HSL), also known as cold sores, on the lips is primarily caused by the herpes simplex virus type 1 (HSV-1) 1. The virus is highly contagious and spreads through direct contact with an infected person's saliva or skin. You can get a cold sore by kissing someone with an active sore, sharing utensils, towels, or lip products with an infected person, or touching an active sore and then touching your lips. Once infected, the virus remains dormant in your nerve cells and can reactivate due to triggers like stress, illness, fatigue, sun exposure, hormonal changes, or a weakened immune system 1. When reactivated, you may experience tingling or itching before the blister appears. Some of the key factors that contribute to the development of HSL include:

  • Female gender
  • Older age (65–74 years)
  • White race/ethnicity
  • Frequent upper respiratory infections
  • Low lymphocyte counts To prevent transmission, it is essential to:
  • Avoid close contact with infected individuals during outbreaks
  • Not share personal items
  • Wash hands frequently
  • Use lip balm with SPF protection If you have a cold sore, over-the-counter treatments like docosanol (Abreva) can help speed healing, while prescription antivirals such as acyclovir (Zovirax), valacyclovir (Valtrex), or famciclovir (Famvir) are most effective when started at the first sign of symptoms 1. Cold sores typically heal within 7-10 days without treatment, but medications can reduce this time and minimize discomfort. It is crucial to note that primary HSV-1 infection can be either asymptomatic or cause self-limiting gingivostomatitis in the immunocompetent host, and the virus establishes latency in the sensory ganglia, which can reactivate and cause HSL 1. The aim of antiviral therapy is to block viral replication to enable shortening the duration of symptoms and to accelerate healing of the lesions associated with HSL.

From the Research

Causes of Herpes Simplex Labialis (HSL)

  • Herpes Simplex Labialis (HSL), also known as cold sores, is a common disease of the lips caused by the herpes simplex virus 2
  • The virus is usually transmitted during childhood via nonsexual contact, and most infections involve the oral mucosa or lips (herpes labialis) 3
  • Adults who are uninfected in childhood may be exposed to the virus, for example, by kissing, and develop an acute primary herpes with fever and gingivo-stomatitis 4

Transmission and Risk Factors

  • Herpes simplex virus type 1 is a highly contagious and widespread infection 5
  • The virus can be transmitted through skin-to-skin contact, such as kissing or sharing utensils 3
  • Recurrent infections can be triggered by various factors, including stress, fatigue, and exposure to sunlight 2

Clinical Manifestations

  • HSL presents as a painful vesicular eruption, forming unsightly crusts, which cause cosmetic disfigurement and psychosocial distress 2
  • The diagnosis of an infection with herpes simplex virus type 1 is usually made by the appearance of the lesions (grouped vesicles or ulcers on an erythematous base) and patient history 3
  • Other clinical manifestations of herpes simplex virus type 1 infections include herpetic keratitis, herpetic whitlow, herpes gladiatorum, and herpetic sycosis of the beard area 3

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Research

Interventions for prevention of herpes simplex labialis (cold sores on the lips).

The Cochrane database of systematic reviews, 2015

Research

Nongenital herpes simplex virus.

American family physician, 2010

Research

[Prevention and treatment of Herpes Labialis].

Journal de pharmacie de Belgique, 2016

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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