Some studies in Australia, Brazil and Germany pointed to alcohol-containing mouthwashes as also being potential causes. The claim was that constant exposure to these alcohol-containing rinses, even in the absence of smoking and drinking, leads to significant increases in the development of oral cancer. However, studies conducted in 1985, 1995, and 2003 summarize that alcohol-containing mouth rinses are not associated with oral cancer. In a March 2009 brief, the American Dental Association said "the available evidence does not support a connection between oral cancer and alcohol-containing mouthrinse". A 2008 study suggests that acetaldehyde (a breakdown product of alcohol) is implicated in oral cancer, but this study specifically focused on abusers of alcohol and made no reference to mouthwash. Any connection between oral cancer and mouthwash is tenuous without further investigation.

In a study of Europeans, smoking and other tobacco use was associated with about 75 percent of oral cancer cases, caused by irritation of the mucous membranes of the mouth from smoke and heat of cigarettes, cigars, and pipes. Tobacco contains over 60 known carcinogens, and the combustion of it, and by-products from this process, is the primary mode of involvement. Use of chewing tobacco or snuff causes irritation from direct contact with the mucous membranes.

Tobacco use in any form by itself, and even more so in combination with heavy alcohol consumption, continues to be an important risk factor for oral cancer. However, due to the current trends in the spread of HPV16, as of early 2011 the virus is now considered the primary causative factor in 63% of newly diagnosed patients.

Erythroplakia has an unknown cause but researchers presume it to be similar to the causes of squamous cell carcinoma. Carcinoma is found in almost 40% of erythroplakia. It is mostly found in elderly men around the ages of 65 - 74. It is commonly associated with smoking.

Alcohol and tobacco use have been described as risk factors.

Tobacco smoking or chewing is the most common causative factor, with more than 80% of persons with leukoplakia having a positive smoking history. Smokers are much more likely to suffer from leukoplakia than non-smokers. The size and number of leukoplakia lesions in an individual is also correlated with the level of smoking and how long the habit has lasted for. Other sources argue that there is no evidence for a direct causative link between smoking and oral leukoplakia. Cigarette smoking may produce a diffuse leukoplakia of the buccal mucosa, lips, tongue and rarely the floor of mouth. Reverse smoking, where the lit end of the cigarette is held in the mouth is also associated with mucosal changes. Tobacco chewing, e.g. betel leaf and areca nut, called paan, tends to produce a distinctive white patch in a buccal sulcus termed "tobacco pouch keratosis". In the majority of persons, cessation triggers shrinkage or disappearance of the lesion, usually within the first year after stopping.

Although the synergistic effect of alcohol with smoking in the development of oral cancer is beyond doubt, there is no clear evidence that alcohol is involved in the development of leukoplakia, but it does appear to have some influence. Excessive use of a high alcohol containing mouth wash (> 25%) may cause a grey plaque to form on the buccal mucosa, but these lesions are not considered true leukoplakia.

When associated with the lung, it is typically a centrally located large cell cancer (non-small cell lung cancer or NSCLC). It often has a paraneoplastic syndrome causing ectopic production of parathyroid hormone-related protein (PTHrP), resulting in hypercalcemia, however paraneoplastic syndrome is more commonly associated with small cell lung cancer.

It is primarily due to smoking.

Human papillomavirus infection (HPV) has been associated with SCC of the oropharynx, lung, fingers and anogenital region.

Around 75% of cases are caused by alcohol and tobacco use.

Tobacco smoke is one of the main risk factors for head and neck cancer and one of the most carcinogenic compounds in tobacco smoke is acrylonitrile. (See Tobacco smoking). Acrylonitrile appears to indirectly cause DNA damage by increasing oxidative stress, leading to increased levels of 8-oxo-2'-deoxyguanosine (8-oxo-dG) and formamidopyrimidine in DNA (see image). Both 8-oxo-dG and formamidopyrimidine are mutagenic. DNA glycosylase NEIL1 prevents mutagenesis by 8-oxo-dG and removes formamidopyrimidines from DNA.

However, cigarette smokers have a lifetime increased risk for head and neck cancers that is 5- to 25-fold increased over the general population.

The ex-smoker's risk for squamous cell cancer of the head and neck begins to approach the risk in the general population twenty years after smoking cessation. The high prevalence of tobacco and alcohol use worldwide and the high association of these cancers with these substances makes them ideal targets for enhanced cancer prevention.

Smokeless tobacco is cause of oral and pharyngeal cancers (oropharyngeal cancer). Cigar smoking is an important risk factor for oral cancers as well.

Other environmental carcinogens suspected of being potential causes of head and neck cancer include occupational exposures such as nickel refining, exposure to textile fibers, and woodworking. Use of marijuana, especially while younger, is linked to an increase in squamous-cell carcinoma cases while other studies suggest use is not shown to be associated with oral squamous cell carcinoma, or associated with decreased squamous cell carcinoma.

The incidence of squamous cell carcinoma continues to rise around the world. A recent study estimated that there are between 180,000 and 400,000 cases of SCC in the United States in 2013. Risk factors for squamous cell carcinoma varies with age, gender, race, geography, and genetics. The incidence of SCC increases with age and the peak incidence is usually around 60 years old. Males are affected with SCC at a ratio of 2:1 in comparison to females. Caucasians are more likely to be affected, especially those with fair Celtic skin and chronically exposed to UV radiation. Squamous cell carcinoma of the skin is the most common among all sites of the body. Solid organ transplant recipients (heart, lung, liver, pancreas, among others) are also at a heightened risk of developing aggressive, high-risk SCC. There are also a few rare congenital diseases predisposed to cutaneous malignancy. In certain geographic locations, exposure to arsenic in well water or from industrial sources may significantly increase the risk of SCC.

Immunotherapy with immune checkpoint inhibitors is being investigated in head and neck cancers.

The long-term outcome of squamous cell carcinomas is dependent upon several factors: the sub-type of the carcinoma, available treatments, location(s) and severity, and various patient health-related variables (accompanying diseases, age, etc.). Generally, the long-term outcome is positive, as less than 4% of Squamous cell carcinoma cases are at risk of metastasis. Some particular forms of squamous cell carcinomas have a higher mortality rate. One study found squamous cell carcinoma of the penis had a much greater rate of mortality than some other forms of squamous cell carcinoma, that is, about 23%, although this relatively high mortality rate may be associated with possibly latent diagnosis of the disease due to patients avoiding genital exams until the symptoms are debilitating, or refusal to submit to a possibly scarring operation upon the genitalia. Squamous cell carcinoma occurring in the organ transplant population is also associated with a higher risk of mortality.

Lymphoma is the most common type of blood-related cancer in horses and while it can affect horses of all ages, it typically occurs in horses aged 4–11 years.

STK is extremely common among smokeless tobacco users. Given the association with smokeless tobacco use, this condition tends to occur in adults. A national USA survey estimated an overall prevalence of 1.5% of all types of smokeless tobacco lesions, with males affected more commonly than females.

Usually this lesion is reversible if the tobacco habit is stopped completely, even after many years of use. In one report, 98% of lesions disappeared within 2 weeks of stopping tobacco use. The risk of the lesion developing into oral cancer (generally squamous cell carcinoma and its variant verrucous carcinoma) is relatively low. Indeed, veruccous carcinoma is sometimes term snuff dipper's cancer. In most reported cases, malignant transformation has occurring in individuals with a very long history of chewing tobacco or who use dry snuff.

Smokeless tobacco use is also accompanied by increased risk of other oral conditions such as dental caries (tooth decay), periodontitis (gum disease), attrition (tooth wear) and staining.

Head and neck cancers are malignant neoplasms that arise in the head and region which comprises nasal cavity, paranasal sinuses, oral cavity, salivary glands, pharynx, and larynx. Majority of head and neck cancers histologically belong to squamous cell type and hence they are categorized as Head and Neck Squamous Cell Carcinoma (abbreviated as HNSCC)[Forastiere AA, 2003]. HNSCC are the 6th most common cancers worldwide and 3rd most common cancers in developing world. They account for ~ 5% of all malignancies worldwide (Ferlay J, 2010) and 3% of all malignancies in the United States (Siegel R, 2014).

Risk factors include tobacco consumption (chewing or smoking), alcohol consumption, Epstein-Barr virus (EBV) infection, human papilloma virus (HPV; esp. HPV 16, 18) infection, betel nut chewing, wood dust exposures, consumption of certain salted fish and others (NCI Factsheet, 2013). EBV infection has been specifically associated with nasopharyngeal cancer. Reverse smoking was considered as a risk factor for oral cancer. Interestingly, "Cis-retinoic acid" (i.e. supplements of retinoic acid) intake may increase the risk of HNSCC in active smokers. Low consumption of fruits and vegetables was associated with higher incidence of HNSCC.

HNSCC classification: Based on the HPV infection status, head and neck cancers are classified into HPV-positive and HPV-negative categories. So far, this is the only available molecular classification. Majority (>50%) of oral cancers are HPV-positive in the U.S. HPV-positive oral cancers are widely prevalent in younger patients and are associated with multiple sexual partners and oral sexual practices. HPV-positive cancers have better prognosis, especially for nonsmokers as compared to HPV-negative cancers.

Staging and grading of HNSCC: HNSCC are classified according to the tumor-node-metastasis (TNM) system of American Joint Committee on cancer. TNM staging system for HNSCC are discussed else where.

Symptoms include lump or sore, sore throat, hoarse of voice, difficulty in swallowing etc (NCI Factsheet, 2013).

Treatment for HNSCC is predominantly based on the stage of the disease. Factors such as patient fitness, baseline swallow, airway functional status, and others are considered before determining the treatment plan. Standard of care for HNSCC includes one or combination of the following: surgery, radiation, chemotherapeutic agents such as Cisplatin, 5-Flurouracil (5-FU) etc. Molecularly targeted therapies were developed since the discovery of role of epidermal growth factor receptor (EGFR) signaling in HNSCC development, progression and prognosis. These targeted therapies include monoclonal antibodies (such as cetuximab, panitumumab etc.) and tyrosine kinase inhibitors (such as erlotinib, gefitinib, etc.). Among these EGFR-targeting agents, only cetuximab has been approved by FDA in 2006 for HNSCC treatment.

Ninety percent (MacMillan, 2015) of cases of head and neck cancer (cancer of the mouth, nasal cavity, nasopharynx, throat and associated structures) are due to squamous cell carcinoma. Symptoms may include a poorly healing mouth ulcer, a hoarse voice or other persistent problems in the area. Treatment is usually with surgery (which may be extensive) and radiotherapy. Risk factors include smoking, alcohol consumption and hematopoietic stem cell transplantation (Elad S, Zadik Y, Zeevi I, et al., 2010, pp. 1243–1244). In addition, recent studies show that about 25% of mouth and 35% of throat cancers are associated with HPV. The 5 year disease free survival rate for HPV positive cancer is significantly higher when appropriately treated with surgery, radiation and chemotherapy as compared to non-HPV positive cancer, substantiated by multiple studies including research conducted by Maura Gillison, "et al." of Johns Hopkins Sidney Kimmel Cancer Center.

Treatment involves biopsy of the lesion to identify extent of dysplasia. Complete excision of the lesion is sometimes advised depending on the histopathology found in the biopsy. Even in these cases, recurrence of the erythroplakia is common and, thus, long-term monitoring is needed.

It is an uncommon condition, occurring with equal prevalence in males and females and at any age.

Tumors related to squamous-cell carcinoma (SCC) can appear anywhere on the body, but they are most often located in non-pigmented skin near mucocutaneous junctions (where skin meets mucous membranes) such as on the eyelids, around the nostrils, lips, vulva, prepuce, penis or anus. The tumors are raised, fleshy, often ulcerated or infected and may have an irregular surface. Rarely, primary SCC develops in the esophagus, stomach (non-glandular portion), nasal passages and sinuses, the hard palate, gums, guttural pouches and lung. The eyelid is the most common site, accounting for 40-50% of cases, followed by male (25-10% of cases) and female (10% of cases) genitalia. Horses with lightly pigmented skin, such as those with a gray hair coat or white faces, are especially prone to developing SCC, and some breeds, such as Clydesdales, may have a genetic predisposition. Exposure of light-colored skin to UV light has often been cited as a predisposing factor, but lesions can occur in dark skin and in areas that are not usually exposed to sunlight, such as around the anus. Buildup of smegma ("the bean" in horseman's terms) on the penis is also linked to SCC and is thought to be a carcinogen through penile irritation. Pony geldings and work horses are more prone to developing SCC on the penis, due to less frequent penile washing when compared to stallions. Equine papillomavirus-2 has also been found within penile SCCs, but has not been determined to cause SCC.

AC is caused by chronic and excessive exposure to ultraviolet radiation in sunlight.

Risk factors include:

- Outdoor lifestyle: e.g. farmers, sailors, fishermen, windsurfers, mountaineers, golfers, etc. This has given rise to synonyms for this condition such as "sailor's lip" and "farmer's lip". The prevalence in agricultural workers in a semi-arid region of Brazil is reported to be 16.7%.

- Light skin complexion: the condition typically affects individuals with lighter skin tones, particularly Caucasians living in tropical regions. In one report, 96% of persons with AC had phenotype II according to the Fitzpatrick scale.

- Age: AC typically affects older individuals, and rarely those under the age of 45.

- Gender: the condition affects males more commonly than females. Sometimes this ratio is reported as high as 10:1.

Additional factors may also play a role, including tobacco use, lip irritation, poor oral hygiene, and ill-fitting dentures.

Leukoedema is common. It occurs in about 70-90% of black skinned adults and about 50% of black skinned children. The prevalence in white skinned people is considerably less, but reports range from less than 10% to more than 90%, probably varying depending upon the population studied, and the methods used in the study, e.g. examination conditions and the diagnostic criteria. The ethnic variation may be explained by genetic factors or simply because black skinned people have greater amount of melanin in the mucosa, making it appear darker (termed racial or physiologic pigmentation). This darker mucosa may make the edematous changes more noticeable, whereas in the mucosa of people with lighter skin types leukoedema gives a milder presentation.

The cause is unknown, but it is thought to be caused by intracellular edema of the superficial epithelial cells coupled with retention of superficial parakeratin. Although leukoedema is thought to be a developmental condition, it may be more common and more pronounced in smokers, and becomes less noticeable when smoking is stopped. Smoking cannabis is known to be linked to this condition. It may also develop in areas subjecte to repeat subclinical irritation, caused by low grade irritants such as spices, oral debris or tobacco.

The lesion is usually present in children. Ranulas are the most common pathologic lesion associated with the sublingual glands.

To prevent AC from developing, protective measures could be undertaken such as avoiding mid-day sun, or use of a broad-brimmed hat, lip balm with anti UVA and UVB ingredients (e.g. para-aminobenzoic acid), or sun blocking agents (e.g. zinc oxide, titanium oxide) prior to sun exposure.

Treatment may include the following:

- Surgery with or without radiation

- Radiotherapy

Fast neutron therapy has been used successfully to treat salivary gland tumors, and has shown to be significantly more effective than photons in studies treating unresectable salivary gland tumors.

- Chemotherapy

The main medical risk factors are having bladder cancer or having conditions that cause chronic inflammation in the urethra. People over the age of 60 and white women have the highest risks.