The known risk factors are determined by the basic constitution of the patient and by types of external aggression that are harmful to health. People who:

• have little melanin (pigment protecting against the sun)
• have a fair complexion or red hair
• burn easily when exposed to the sun

are 20 to 30 times more likely to develop skin cancer in their lifetime than those with dark complexions who tan easily.

• People with atypical nevi (irregular-shaped moles of a larger than usual size) or a large number of such moles (more than 20) should check with their dermatologist for possible skin cancer symptoms. This type of patient may also have a personal or family background in skin cancer, factors which in themselves represent a greater risk.
• Patients with a deficient immune system (natural defenses), whether due to illness or medicine taken to prevent organ transplant rejection, for example, have "weaker" resistance to the appearance of a cutaneous tumor.
• The most studied type of agression is solar radiation. The influence of sunburn (especially in childhood) on the possible future development of skin cancer is well known: the more sunburn the greater the likelihood (consult the relevant section in the book "Cuando calienta el sol" – "When the Sun Shines")