A variety of medical issues, though uncommon, can result from tattooing. Because it requires breaking the skin barrier, tattooing may carry health risks, including infection and allergic reactions. Modern tattooists reduce such risks by following universal precautions, working with single-use items, and sterilising their equipment after each use. Many jurisdictions require that tattooists have bloodborne pathogen training, such as is provided through the Red Cross and OSHA.
Dermatologists have observed rare but severe medical complications from tattoo pigments in the body, and have noted that people acquiring tattoos rarely assess health risks prior to receiving their tattoos. Some medical practitioners have recommended greater regulation of pigments used in tattoo ink. The wide range of pigments currently used in tattoo inks may create unforeseen health problems.
Infection
Since tattoo instruments come in contact with blood and bodily fluids, diseases may be transmitted if the instruments are used on more than one person without being sterilised. However, infection from tattooing in clean and modern tattoo studios employing single-use needles is rare. With amateur tattoos, such as those applied in prisons, however, there is an elevated risk of infection. To address this problem, a programme was introduced in Canada as of the summer of 2005 that provides legal tattooing in prisons, both to reduce health risks and to provide inmates with a marketable skill. Inmates were to be trained to staff and operate the tattoo parlours once six of them opened successfully.
In the United States, the Red Cross prohibits a person who has received a tattoo from donating blood for 12 months (FDA 2000), unless the procedure was done in a state-regulated and licensed studio, using sterile technique. Not all states have a licensing program, meaning that people who receive tattoos in those states are subject to the 12-month deferral regardless of the hygienic standards of the studio. Similarly, the UK does not provide certification for tattooists, and blood donations are prohibited without exception for six months following a tattoo.
Infections that can theoretically be transmitted by the use of unsterilised tattoo equipment or contaminated ink include surface infections of the skin, hepatitis B, hepatitis C, tuberculosis, and HIV. However, no person in the United States is reported to have contracted HIV via a commercially-applied tattooing process. Washington state's OSHA studies have suggested that since the needles used in tattooing are not hollow, in the case of a needle stick injury the amount of fluids transmitted may be small enough that HIV would be difficult to transmit. Tetanus risk is reduced by having an up-to-date tetanus booster prior to being tattooed. According to the Centers for Disease Control and Prevention no data indicates an association between tattooing in the United States and increased risk for HCV infection.
In 2006, the CDC reported 3 clusters with 44 cases of methicillin-resistant staph infection traced to unlicensed tattooists.
Reactions to inks
Perhaps due to the mechanism whereby the skin's immune system encapsulates pigment particles in fibrous tissue, tattoo inks have been described as "remarkably nonreactive histologically". However, some allergic reactions have been medically documented. No estimate of the overall incidence of allergic reactions to tattoo pigments exists. Allergies to latex are apparently more common than to inks; many artists will use non-latex gloves when requested.
Allergic reactions to tattoo pigments, while uncommon, are most often seen with red, yellow, and occasionally white. Reactions can be triggered by exposure to sunlight. People who are sensitive or allergic to certain metals may react to pigments in the skin with swelling and/or itching, and/or oozing of clear fluid called serum. Such reactions are quite rare, however, and some artists will recommend performing a test patch. Because the mercury and Azo-chemicals in red dyes are more commonly allergenic than other pigments, allergic reactions are most often seen in red tattoos. Less frequent allergic reactions to black, purple, and green pigments have also been noted.
Traditional metallic salts are prevalent in tattoo inks. A 3x5 inch tattoo may contain from 1 to 23 micrograms of lead; lead exposure has been linked to birth defects, cancer, and other reproductive harm. Organic pigments (i.e., non-heavy metal pigments) may also pose health concerns. A European Commission noted that close to 40% of organic tattoo colorants used in Europe had not been approved for cosmetic use, and that under 20% of colorants contained acarcinogenic aromatic amine.
MRI complications
A few cases of burns on tattoos caused by MRI scans have been documented. Problems tend to occur with designs containing large areas of black ink, since black commonly contains iron oxide; the MRI scanner causes the iron to heat up either by inducing an electrical current or hysteresis. Burning can occur on smaller tattoos such as "permanent makeup", but this is rare. Non-ferrous pigments have also been known to cause burns during an MRI. It should be stressed that tattoo burns are rare, so merely having a tattoo should not be a cause to not get an MRI scan if necessary.
Dermal conditions
The most common dermal reactions to tattoo pigments are granulomas and various lichenoid diseases. Other conditions noted have been cement dermatitis, collagen deposits, discoid lupus erythematosus, eczematous eruptions,hyperkeratosis and parakeratosis, and keloids.
Delayed reactions
Hypersensitive reactions to tattoos are known to lay latent for significant periods of time before exhibiting symptoms. Delayed abrupt chronic reactions, such as eczematous dermatitis, are known to manifest themselves from months to as many as twenty years after the patient received his or her most recent tattoo.
Azo-type pigments used in tattoos tend to cleave through enzymatic catalysis of redox reactions, resulting in highly electrophilic aromatic amine by-products capable of covalently binding with DNA. Napthol and Azos break down in sunlight exposure into toxic and/or carcinogenic aromatic amines. As with heavy metals, these by-products of the pigments’ decomposition accumulate in the lymphatic system. Plastic-based inks (e.g., glow-in-the-dark ink) are known to lead topolymerisation under the skin, where the tattoo pigment particles converge into one solid plastic piece under the skin.
Other adverse effects
Other documented conditions caused by tattoo pigments have been carcinoma, hyperplasia, tumours, and vasculitis. Keratoacanthoma may also occur, which makes excision of the affected area mandatory.
Haematoma
Occasionally, when a blood vessel is punctured during the tattooing procedure a haematoma may appear. Bruises generally heal within one week. Bruises can appear as halos around a tattoo, or if blood pools, as one larger bruise.
Burden on lymphatic system
Some pigment migrates from a tattoo site to lymph nodes, where large particles may accumulate. When larger particles accumulate in the lymph nodes, inflammation may occur. Smaller particles, such as those created by laser tattoo treatments, are small enough to be carried away by the lymphatic system and not accumulate.
Interference with melanoma diagnosis
Lymph nodes may become discoloured and inflamed with the presence of tattoo pigments, but discoloration and inflammation are also visual indicators of melanoma; consequently, diagnosing melanoma in a patient with tattoos is made difficult, and special precautions must be taken to avoid misdiagnoses.