Sunless tanning
Sunless tanning (also known as self tanning, or UV-free tanning) refers to applying chemicals on the skin to produce an effect similar in appearance to a traditional suntan. Sunless tanning arose in response to links between sun exposure and skin cancer discovered in the 1960s, along with other alternatives to natural sun tanning such as the use of a sunbed or tanning bed.

# DHA-based products
According to the American Academy of Dermatology, the most effective products available are sunless tanning or self tanning lotions that contain dihydroxyacetone (DHA) as the active ingredient. The tan is not a dye, stain or paint, but a chemical reaction between the DHA and the amino acids in the dead layer on the skin surface. This is similar to a reaction which is well known to food chemists and is called the Maillard reaction. This refers to the browning process during food manufacturing and storage. It does not involve skin pigmentation nor does it need UV exposure to initiate the color change.
The reaction is non-toxic and skin safe, without the damage associated with UV exposure. The tan is temporary and will fade gradually over 3 to 10 days. 
Some products use Erythrulose combined with the DHA. Erythrulose works identically to DHA on the skin surface, but develops more slowly. The two chemicals used together may produce a longer lasting sunless tan.
Dihydroxyacetone or Erythrulose may cause contact dermatitis. First time users of sunless tanning products should apply them to a small patch of skin and wait 24 hours before a full body application.
These products can be applied at home, in the form of gels, lotions, mousses, sprays and wipes. Best results are obtained when applied to clean, dry skin. Bathing and swimming should be avoided until product is fully absorbed, which varies from one to six hours. More DHA is absorbed by the thicker skin on the hands and feet, so those areas should be skipped or cleaned immediately after application.
Professional application options are available from spas, salons, and gymnasiums in the form of sunless or UV-Free spray booths. The enclosed booth, which resembles an enclosed shower stall, sprays the sunless tanning solution over the entire body.
Airbrush spray tans are applied by professional technicians using specialized equipment designed for applying self tanning sprays, such as an airbrush, LVLP spraygun, and HVLP spraygun equipment types. The technician hand sprays the client from head to toe with a gentle solution misting.
DHA has been approved for cosmetic use by the Food and Drug Administration (FDA), the Canadian Health Ministry and most of the EU member nations. It is considered nontoxic and noncarcinogenic. Because DHA does not use the skin's melanocytes to make the skin a tan color it is recommended as a cosmetic disguising cover for Vitiligo patients.
DHA based Sunless tanning has been recommended by the Skin Cancer Organization, American Academy of Dermatology, Canadian Dermatology Association, The American Cancer Society and the American Medical Association.

# Tyrosine-based products
Although gels, lotions or sprays that contain DHA are said to be the most reliable and useful, there are other types of products on the market. Tanning accelerators -- lotions or pills that usually contain the amino acid tyrosine -- claim that they stimulate and increase melanin formation, thereby accelerating the tanning process. These are used in conjunction with UV exposure. At this time, there is no scientific data available to support these claims.

# Canthaxanthin-based products
Another sunless-tanning product is a tanning pill that contains canthaxanthin, which is most commonly used as a color additive in certain foods. Although the FDA has approved the use of canthaxanthin in food, it does not approve its use as a tanning agent. When used as a color additive, only very small amounts of canthaxanthin are necessary. As a tanning agent, however, much larger quantities are used. After canthaxanthin is consumed, it is deposited throughout the body, including in the layer of fat below the skin, which turns an orange-brown color. These types of tanning pills have been linked to various side effects, including hepatitis and canthaxanthin retinopathy, a condition in which yellow deposits form in the retina of the eye. Side effects including damage to the digestive system and skin surface have also been noted. The FDA withdrew approval for use of canthaxanthin as a tanning agent, and has issued warnings concerning its use. 

# Melanotan hormone
Melanotan, a melanocyte-stimulating hormone, which induces skin pigment increase and tanning, is another alternative on the horizon. This drug has not yet been approved for clinical trials in the USA, although it has been extensively tested in Australia. Melanotan may require some UV exposure to be most effective.

# Temporary bronzers
Bronzers are a temporary sunless tanning or bronzing option. These come in powders, sprays, gels, lotions and moisturizers. Once applied, they create a tan that can easily be removed with soap and water. Like make-up, these products tint or stain your skin only until they are washed off.
They are often used for a "one-day" only tan, or to complement a DHA based sunless tan. Many formulations are available, and some have limited sweat or light water resistance. Most will create some light but visible rub-off onto snug clothing. Therefore they should not be applied under clothing, or where fabric and skin edges meet. Dark clothing will prevent the rub-off from being noticeable.