A tan is your skin recording an injury

Tanning, outdoors or in a bed, is not healthy. The reason is mechanical rather
than moralistic, and it is worth understanding once.

Sunlight arrives as visible and invisible rays. Ultraviolet rays are a
form of radiation, and two types reach the earth's surface and your skin:

When UVA reaches your skin, the skin tries to protect itself from further
damage by making more melanin — the pigment that darkens it. That darkening
is the tan.

So a tan is a sign of skin damage. Not a risk of damage; a response to
damage that has already happened.

You do need some UV: it is how your body makes vitamin D. Most people get
enough from about 5 to 15 minutes of sun, two or three times a week.

What the damage adds up to

• Premature ageing — thickened, leathery, wrinkled skin and dark spots, as
  long-term UV exposure costs the skin its elasticity. More sun, earlier
  ageing.
• Skin cancers, including melanoma — UV damages the DNA of skin cells and
  interferes with the body's ability to fight the cancer.
• Actinic keratosis — a thick scaly patch, usually on the face, scalp,
  backs of the hands or chest, which can eventually become cancerous.
• Eye damage — cataracts and photokeratitis (snow blindness).
• A weakened immune system — which raises sensitivity to sunlight,
  decreases the effect of vaccines, and can cause reactions to certain
  medicines.

Indoor tanning is worse, not safer

**Tanning beds use UVA light, so they expose you to a higher concentration of
UVA than the sun would** — plus some UVB. Two more things follow:

• A "base tan" protects nobody. It is damage to the skin, and it will not
  stop you burning outside.
• It is particularly dangerous young. Starting indoor tanning as a teenager
  or young adult carries a higher melanoma risk. Some research suggests
  frequent tanning may be addictive, which matters because the more often you
  tan the more damage accumulates.

Protecting your skin

• Limit exposure between 10 a.m. and 4 p.m. — remembering that cloudy days
  and shade still deliver sun.
• Sunscreen, SPF 15 or higher, and broad-spectrum so it covers UVA as
  well as UVB. SPF 30 or higher for very light skin. Apply **20–30 minutes
  before** going out and reapply at least every 2 hours.
• Sunglasses blocking UVA and UVB; wrap-around styles stop rays entering
  from the side.
• A wide-brimmed hat in tightly woven fabric such as canvas.
• Long sleeves, long trousers or skirts, tightly woven.
• Check your skin once a month, and see a provider about any new or
  changing spot or mole.

Looking tan without the damage

• Tanning pills contain a colour additive that turns skin orange. They can
  be dangerous and are not FDA approved.
• Sunless tanners — most spray tans, lotions and gels use DHA, which
  the FDA considers safe for use on the outside of the body. Keep it out of
  your nose, eyes and mouth, and do not breathe in a spray.

Neither protects you from UV when you go outside.

Source: MedlinePlus, U.S. National Library of Medicine.