Although there have been many technological advances in tattooing, tattoos will always age as the skin ages. Genetics, environment and lifestyle combine to determine both the skin's long term health and the appearance of a tattoo. Even with fastidious care, aging skin tissue loses moisture and elasticity. A tattoo on dry skin with diminished elasticity will fade and its contours will soften. The more fine detail work in the tattoo's design, the more it will change when the skin ages. Faded and softened tattoos do not show detail or shading as well, and the smaller the tattoo the more pronounced the effect. For that reason, large tattoos tend to age more gracefully than smaller, intricate designs. Bolder and larger pieces hold up to changes over the years. Trendy, bold tribal tattoos will change very little over time, whereas small, elaborate designs with fine line shading are likely to change dramatically. Just as prolonged exposure to ultraviolet (UV) rays can cause dramatic, irreversible and sometimes deadly skin damage, they also accelerate damage to body art. Sun exposure speeds up line or color decay. Black ink is particularly sensitive to sun exposure. Some black inks fade to gray with extended sun exposure, while others take on a bluish tinge. Occasionally, whites and light yellows disappear if the skin is badly sunburned. One of the key threats to an aging tattoo design does not alter the tattoo itself but is a very real consequence of a simple fact of life - weight fluctuations. The speed of weight gain or weight loss, skin moisture and tattoo placement all influence how well a tattoo withstands weight gain. The more slowly the weight fluctuates, the more skin retains its elasticity. Moisture also helps skin to retain its elasticity. The way a tattoo reacts to weight gain varies widely from person to person, because it depends on where the person carries his or her weight. Areas where the skin remains more taut or areas that have more muscle will hold the design better than sagging or fatty areas. Although most tattoos will change shape when the skin is stretched or contracted, torso tattoos are arguably the most susceptible to irreparable damage after weight gain. A tattoo artist's skill and equipment can change a tattoo's long term durability. A well trained tattoo artist can bring considerable craftsmanship to the boldest and simplest tattoos. There is a wide variety in the resilience of tattoo inks as well. Tattoo inks consist of simple carbon particles. The carbon base usually comes from burnt wood, cotton, vegetables, India or pen ink and plastic. Professional artists have access to more than 100 different colors.