Shingles can be confused with herpes simplex, dermatitis herpetiformis and impetigo, and skin reactions caused by contact dermatitis, candidiasis, certain drugs and insect bites.

The likelihood of the infection being spread can be reduced through behaviors such as avoiding touching an active outbreak site, washing hands frequently while the outbreak is occurring, not sharing items that come in contact with the mouth, and not coming into close contact with others (by avoiding kissing, oral sex, or contact sports).

Because the onset of an infection is difficult to predict, lasts a short period of time and heals rapidly, it is difficult to conduct research on cold sores. Though famciclovir improves lesion healing time, it is not effective in preventing lesions; valaciclovir and a mixture of acyclovir and hydrocortisone are similarly useful in treating outbreaks but may also help prevent them.

Acyclovir and valacyclovir by mouth are effective in preventing recurrent herpes labialis if taken prior to the onset of any symptoms or exposure to any triggers. Evidence does not support L-lysine.

Primary orofacial herpes is readily identified by clinical examination of persons with no previous history of lesions and contact with an individual with known HSV-1 infection. The appearance and distribution of sores in these individuals typically presents as multiple, round, superficial oral ulcers, accompanied by acute gingivitis. Adults with atypical presentation are more difficult to diagnose. Prodromal symptoms that occur before the appearance of herpetic lesions help differentiate HSV symptoms from the similar symptoms of other disorders, such as allergic stomatitis. When lesions do not appear inside the mouth, primary orofacial herpes is sometimes mistaken for impetigo, a bacterial infection. Common mouth ulcers (aphthous ulcer) also resemble intraoral herpes, but do not present a vesicular stage.

Genital herpes can be more difficult to diagnose than oral herpes, since most HSV-2-infected persons have no classical symptoms. Further confusing diagnosis, several other conditions resemble genital herpes, including fungal infection, lichen planus, atopic dermatitis, and urethritis. Laboratory testing is often used to confirm a diagnosis of genital herpes. Laboratory tests include culture of the virus, direct fluorescent antibody (DFA) studies to detect virus, skin biopsy, and polymerase chain reaction to test for presence of viral DNA. Although these procedures produce highly sensitive and specific diagnoses, their high costs and time constraints discourage their regular use in clinical practice.

Until the 1980s serological tests for antibodies to HSV were rarely useful to diagnosis and not routinely used in clinical practice. The older IgM serologic assay could not differentiate between antibodies generated in response to HSV-1 or HSV-2 infection. However, a glycoprotein G-specific (IgG) HSV test introduced in the 1980s is more than 98% specific at discriminating HSV-1 from HSV-2.

It should not be confused with conditions caused by other viruses in the "herpesviridae" family such as herpes zoster, which is caused by varicella zoster virus. The differential diagnosis includes hand, foot and mouth disease due to similar lesions on the skin.

Treatment includes fluid intake, good oral hygiene and gentle debridement of the mouth, as well as oral acyclovir. In healthy individuals the lesions heal spontaneously in 7–14 days without scarring.

Antivirals may reduce asymptomatic shedding; asymptomatic genital HSV-2 viral shedding is believed to occur on 20% of days per year in patients not undergoing antiviral treatment, "versus" 10% of days while on antiviral therapy.

Testing peoples blood, including those who are pregnant, who do not have symptoms for HSV is not recommended. This is due to concerns of greater harm than benefit such as relationship problems in the setting of a high rate of tests that may be falsely positive.

If the rash has appeared, identifying this disease (making a differential diagnosis) requires only a visual examination, since very few diseases produce a rash in a dermatomal pattern (see map). However, herpes simplex virus (HSV) can occasionally produce a rash in such a pattern (zosteriform herpes simplex). The Tzanck smear is helpful for diagnosing acute infection with a herpes virus, but does not distinguish between HSV and VZV.

When the rash is absent (early or late in the disease, or in the case of zoster sine herpete), shingles can be difficult to diagnose. Apart from the rash, most symptoms can occur also in other conditions.

Laboratory tests are available to diagnose shingles. The most popular test detects VZV-specific IgM antibody in blood; this appears only during chickenpox or shingles and not while the virus is dormant. In larger laboratories, lymph collected from a blister is tested by polymerase chain reaction for VZV DNA, or examined with an electron microscope for virus particles. Molecular biology tests based on in vitro nucleic acid amplification (PCR tests) are currently considered the most reliable. Nested PCR test has high sensitivity, but is susceptible to contamination leading to false positive results. The latest real-time PCR tests are rapid, easy to perform, and as sensitive as nested PCR, and have a lower risk of contamination. They also have more sensitivity than viral cultures.

Docosanol, a saturated fatty alcohol, is a safe and effective topical application that has been approved by the United States Food and Drug Administration for herpes labialis in adults with properly functioning immune systems. It is comparable in effectiveness to prescription topical antiviral agents. Due to its mechanism of action, there is little risk of drug resistance. The duration of symptoms can be shortened a bit if an antiviral, anesthetic, zinc oxide or zinc sulfate cream is applied soon after it starts.

Effective antiviral medications include acyclovir and penciclovir, which can speed healing by as much as 10%. Famciclovir or valacyclovir, taken in pill form, can be effective using a single day, high-dose application and is more cost effective and convenient than the traditional treatment of lower doses for 5–7 days.

A specific clinical diagnosis of HSV as the cause of dendritic keratitis can usually be made by ophthalmologists and optometrists based on the presence of characteristic clinical features. Diagnostic testing is seldom needed because of its classic clinical features and is not useful in stromal keratitis as there is usually no live virus. Laboratory tests are indicated in complicated cases when the clinical diagnosis is uncertain and in all cases of suspected neonatal herpes infection:

- Corneal smears or impression cytology specimens can be analyzed by culture, antigen detection, or fluorescent antibody testing. Tzanck smear, i.e.Papanicolaou staining of corneal smears, show multinucleated giant cells and intranuclear inclusion bodies, however, the test is low in sensitivity and specificity.

- DNA testing is rapid, sensitive and specific. However, its high cost limits its use to research centers.

- Demonstration of HSV is possible with viral culture.

- Serologic tests may show a rising antibody titer during primary infection but are of no diagnostic assistance during recurrent episodes.

Genital herpes can be spread by viral shedding prior to and following the visual signs of symptoms.

Although it is a self-limited illness, oral or intravenous antiviral treatments, particularly acyclovir, have been used in the management of immunocompromised or severely infected patients. Topical acyclovir has not been shown to be effective in management of herpetic whitlow. Famciclovir has been demonstrated to effectively treat and prevent recurrent episodes. Lancing or surgically debriding the lesion may make it worse by causing a superinfection or encephalitis.

Gingivostomatitis symptoms in infants may wrongly be dismissed as teething. "Coincidentally, primary tooth eruption begins at about the time that infants are losing maternal antibody protection against the herpes virus. Also, reports on teething difficulties have recorded symptoms which are remarkably consistent with primary oral herpetic infection such as fever, irritability, sleeplessness, and difficulty with eating." "Younger infants with higher residual levels of antibodies would experience milder infections and these would be more likely to go unrecognized or be dismissed as teething difficulty."

Gingivostomatitis must also be differentiated from herpangina, another disease that also commonly causes ulcers in the oral cavity of children, but is caused by the Coxsackie A virus rather than a herpes virus. In herpangina, ulcers are usually isolated to the soft palate and anterior pillar of the mouth. In herpetic gingivostomatitis, lesions can be found in these locations, but they are almost always accompanied by ulcerations on the gums, lips, tongue or buccal mucosa and/or by hyperemia, hypertrophy or hemorrhage of the gums.

Treatment of herpes of the eye is different based on its presentation: epithelial keratitis is caused by live virus while stromal disease is an immune response and metaherpetic ulcer results from inability of the corneal epithelium to heal:

A diagnosis can be made from clinical signs and symptoms, and treatment consists of minimizing the discomfort of symptoms. It can be differentiated from herpetic gingivostomatitis by the positioning of vesicles - in herpangina, they are typically found on the posterior oropharynx, as compared to gingivostomatitis where they are typically found on the anterior oropharynx and the mouth.

In children the primary source of infection is the orofacial area, and it is commonly inferred that the virus (in this case commonly HSV-1) is transferred by the cutting, chewing or sucking of fingernail or thumbnail.

In adults, it is more common for the primary source to be the genital region, with a corresponding preponderance of HSV-2. It is also seen in adult health care workers such as dentists because of increased exposure to the herpes virus.

Contact sports are also a potential source of infection with herpetic whitlows.

Diagnosis is mostly based on the clinical appearance and the medical history. The most important diagnostic feature is a history of recurrent, self healing ulcers at fairly regular intervals. Although there are many causes of oral ulceration, "recurrent" oral ulceration has relatively few causes, most commonly aphthous stomatitis, but rarely Behçet's disease, erythema multiforme, ulceration associated with gastrointestinal disease, and recurrent intra-oral herpes simplex infection. A systemic cause is more likely in adults who suddenly develop recurrent oral ulceration with no prior history.

Special investigations may be indicated to rule out other causes of oral ulceration. These include blood tests to exclude anemia, deficiencies of iron, folate or vitamin B12 or celiac disease. However, the nutritional deficiencies may be latent and the peripheral blood picture may appear relatively normal. Some suggest that screening for celiac disease should form part of the routine work up for individuals complaining of recurrent oral ulceration. Many of the systemic diseases cause other symptoms apart from oral ulceration, which is in contrast to aphthous stomatitis where there is isolated oral ulceration. Patch testing may be indicated if allergies are suspected (e.g. a strong relationship between certain foods and episodes of ulceration). Several drugs can cause oral ulceration (e.g. nicorandil), and a trial substitution to an alternative drug may highlight a causal relationship.

Tissue biopsy is not usually required, unless to rule out other suspected conditions such as oral squamous cell carcinoma. The histopathologic appearance is not pathognomonic (the microscopic appearance is not specific to the condition). Early lesions have a central zone of ulceration covered by a fibrinous membrane. In the connective tissue deep to the ulcer there is increased vascularity and a mixed inflammatory infiltrate composed of lymphocytes, histiocytes and polymorphonuclear leukocytes. The epithelium on the margins of the ulcer shows spongiosis and there are many mononuclear cells in the basal third. There are also lymphocytes and histiocytes in the connective tissue surrounding deeper blood vessels near to the ulcer, described histologically as "perivascular cuffing".

Treatment is usually supportive only, as the disease is self-limiting and usually runs its course in less than a week.

Oral and maxillofacial pathology, previously termed oral pathology, is a speciality involved with the diagnosis and study of the causes and effects of diseases affecting the oral and maxillofacial regions (i.e. the mouth, the jaws and the face). It can be considered a speciality of dentistry and pathology. Oral pathology is a closely allied speciality with oral and maxillofacial surgery and oral medicine.

The clinical evaluation and diagnosis of oral mucosal diseases are in the scope of oral & maxillofacial pathology specialists and oral medicine practitioners, both disciplines of dentistry.

When a microscopic evaluation is needed, a biopsy is taken, and microscopically observed by a pathologist. The American Dental Association uses the term oral and maxillofacial pathology, and describes it as "the specialty of dentistry and pathology which deals with the nature, identification, and management of diseases affecting the oral and maxillofacial regions. It is a science that investigates the causes, processes and effects of these diseases."

In some parts of the world, oral and maxillofacial pathologists take on responsibilities in forensic odontology.

By definition, there is no serious underlying medical condition, and most importantly, the ulcers do not represent oral cancer nor are they infectious. However, aphthae are capable of causing significant discomfort. There is a spectrum of severity, with symptoms ranging from a minor nuisance to disabling. Due to pain during eating, weight loss may develop as a result of not eating in severe cases of aphthous stomatitis. Usually, the condition lasts for several years before spontaneously disappearing in later life.

Lab Studies:

- No laboratory work is usually necessary.

- Results of cerebrospinal fluid evaluation are abnormal in 61%.

- Pleocytosis is observed in 46%, elevated protein in 26%, and VZV DNA in 22%.

- These findings are not predictive of the clinical course of postherpetic neuralgia.

- Viral culture or immunofluorescence staining may be used to differentiate herpes simplex from herpes zoster in cases that are difficult to distinguish clinically.

- Antibodies to herpes zoster can be measured. A 4-fold increase has been used to support the diagnosis of subclinical herpes zoster (zoster sine herpete). However, a rising titer secondary to viral exposure rather than reactivation cannot be ruled out.

Imaging studies:

- Magnetic resonance imaging lesions attributable to herpes zoster were seen in the brain stem and cervical cord in 56% (9/16) of patients.

- At three months after onset of herpes zoster, 56% (5/9) of patients with an abnormal magnetic resonance image had developed postherpetic neuralgia.

- Of the seven patients who had no herpes-zoster-related lesions on the magnetic resonance image, none had residual pain.

Diagnosis of mouth ulcers usually consists of a medical history followed by an oral examination as well as examination of any other involved area. The following details may be pertinent: The duration that the lesion has been present, the location, the number of ulcers, the size, the color and whether it is hard to touch, bleeds or has a rolled edge. As a general rule, a mouth ulcer that does not heal within 2 or 3 weeks should be examined by a health care professional who is able to rule out oral cancer (e.g. a dentist, oral physician, oral surgeon, or maxillofacial surgeon). If there have been previous ulcers which have healed, then this again makes cancer unlikely.

An ulcer that keeps forming on the same site and then healing may be caused by a nearby sharp surface, and ulcers that heal and then recur at different sites are likely to be RAS. Malignant ulcers are likely to be single in number, and conversely, multiple ulcers are very unlikely to be oral cancer. The size of the ulcers may be helpful in distinguishing the types of RAS, as can the location (minor RAS mainly occurs on non-keratinizing mucosa, major RAS occurs anywhere in the mouth or oropharynx). Induration, contact bleeding and rolled margins are features of a malignant ulcer. There may be nearby causative factor, e.g. a broken tooth with a sharp edge that is traumatizing the tissues. Otherwise, the person may be asked about problems elsewhere, e.g. ulceration of the genital mucous membranes, eye lesions or digestive problems, swollen glands in neck (lymphadenopathy) or a general unwell feeling.

The diagnosis comes mostly from the history and examination, but the following special investigations may be involved: blood tests (vitamin deficiency, anemia, leukemia, Epstein-Barr virus, HIV infection, diabetes) microbiological swabs (infection), or urinalysis (diabetes). A biopsy (minor procedure to cut out a small sample of the ulcer to look at under a microscope) with or without immunofluorescence may be required, to rule out cancer, but also if a systemic disease is suspected. Ulcers caused by local trauma are painful to touch and sore. They usually have an irregular border with erythematous margins and the base is yellow. As healing progresses, a keratotic (thickened, white mucosa) halo may occur.

Good oral hygiene (thorough tooth brushing and flossing and regular professional cleaning and examination) may be helpful to prevent these disorders. Drinking plenty of water and the production of enough saliva, aid in the reduction of bacterial growth. Minimizing irritants or injury in the mouth when possible can aid in the prevention of glossitis. Avoiding excessive use of any food or substance that irritates the mouth or tongue may also help.

Treatment is cause-related, but also symptomatic if the underlying cause is unknown or not correctable. It is also important to note that most ulcers will heal completely without any intervention. Treatment can range from simply smoothing or removing a local cause of trauma, to addressing underlying factors such as dry mouth or substituting a problem medication. Maintaining good oral hygiene and use of an antiseptic mouthwash or spray (e.g. chlorhexidine) can prevent secondary infection and therefore hasten healing. A topical analgesic (e.g. benzydamine mouthwash) may reduce pain. Topical (gels, creams or inhalers) or systemic steroids may be used to reduce inflammation. An antifungal drug may be used to prevent oral candidiasis developing in those who use prolonged steroids. People with mouth ulcers may prefer to avoid hot or spicy foods, which can increase the pain. Self-inflicted ulceration can be difficult to manage, and psychiatric input may be required in some people.

An April 2013 Cochrane Collaboration meta-analysis of 6 randomized controlled trials (RCTs) investigating oral antiviral medications given within 72 hours after the onset of herpes zoster rash in immunocompetent people for preventing postherpetic neuralgia (PHN) found no significant difference between placebo and acyclovir. Combining four RCTs, 44.1% of the acyclovir treatment group developed herpetic neuralgia whereas 53.3% of the placebo group developed herpetic neuralgia. Heterogeneity between the four RCTs was moderate: Chi =3.36, df = 2 (P=0.19); I = 40%.

Additionally, there was no significant difference in preventing the incidence of PHN found in the one RCT included in the meta-analysis that compared placebo to PO famciclovir treatment within 72 hours of HZ rash onset. Studies using valaciclovir treatment were not included in the meta-analysis.

PHN was defined as pain at the site of the dermatomic rash at 120 days after the onset of rash, and incidence was evaluated at 1, 4, and 6 months after rash onset.

There was a slight reduction in the incidence of pain at 4 weeks after the onset of rash in the aciclovir group (153 study participants with pain out of 347 study participants in the aciclovir group) versus the placebo group (184 study participants with pain out of 345 study participants in the placebo group). Patients who are prescribed PO antiviral agents after the onset of rash should be informed that their chances of developing PHN are no different than those not taking PO antiviral agents.

A randomized controlled trial found that amitriptyline 25 mg per night for 90 days starting within two days of onset of rash can reduce the incidence of postherpetic neuralgia from 35% to 16% (number needed to treat is 6).

Chronic ulcerative stomatitis is a recently discovered condition with specific immunopathologic features. It is characterized by erosions and ulcerations which relapse and remit. Lesions are located on the buccal mucosa (inside of the cheeks) or on the gingiva (gums). The condition resembles Oral lichen planus when biopsied.

The diagnosis is made with Immunofluorescence techniques, which shows circulating and tissue-bound autoantibodies (particulate stratified squamous-epithelium-specific antinuclear antibody) to DeltaNp63alpha protein, a normal component of the epithelium. Treatment is with hydroxychloroquine.