Everyone has moles of different sizes and shades, but not all of them will become cancerous, only a very small percentage of them will. Besides, there is a warning for a mole to become cancerous. If a mole has one of the following conditions, you should be alerted to cancer or malignant change: sudden enlargement recently; color is significantly deeper than before; surface elevation, itching and pain, easy to break down, bleeding, etc.; uneven distribution of pigment on the surface, asymmetric lesions, irregular pigmentation halo or hypopigmentation around; small black dots or satellite damage appearing on the surrounding normal skin. In this case, you should consult with the dermatology department to see if histopathological examination is needed to confirm whether there is cancer. In addition, moles with the following conditions should be frequently noticed and if there are changes, it is also best to consult with a hospital as soon as possible to properly deal with them in order to prevent cancerous changes, including: moles that grow on parts that are often subject to friction, such as shaving areas, perineum and wearing bras, or moles in some special areas, such as pigmented moles under the feet, palms and finger (toe) nails, or moles with a diameter larger than 5 mm, as well as moles that repeatedly infections or moles that are susceptible to trauma.