If you're calculating the benefits of Bikram yoga, your appearance may factor into the equation. You might be concerned that the constant stretching will result in stretch marks, but this is exceedingly unlikely. You can, however, develop stretch marks if you build muscle very quickly, but even this is unlikely unless you pair Bikram with strength training.
Bikram Yoga and Stretching
Bikram yoga is different from most other forms of yoga because you perform the poses in a room of about 105 degrees Fahrenheit. In Bikram, you also hold each pose for an extended period of time -- usually a minute or two -- and this increases the amount of stretching you do. However, stretching in and of itself doesn't typically cause stretch marks, so the risk of stretch marks with Bikram is no higher than with other forms of yoga.
Stretch Mark Causes
Your skin contains collagen and other elastic fibers that enable it to stretch and contract in response to your body size. When the skin stretches too quickly, its elasticity can suffer, causing stretch marks. The marks typically start as red or pink lines, then fade to slightly textured white or gray bands. The stretching has to be sustained over an extended period of time -- such as when you rapidly gain weight over several months -- and stretching your muscles doesn't typically stretch the skin sufficiently to cause stretch marks.
Muscle Development and Stretch Marks
Bikram yoga offers some strength training because your body serves as a source of resistance as you shift from one pose to the next. Rapid muscle development can cause your skin to quickly stretch, leading to stretch marks. However, you're much less likely to get stretch marks with Bikram than you are with weightlifting and other more intense forms of strength training.
Weight Gain and Stretch Marks
Weight gain -- especially if it occurs rapidly -- is likely to cause stretch marks. Pregnant women, for example, frequently notice stretch marks on their abdomens. Bikram yoga by itself won't cause you to gain weight and is therefore unlikely to yield stretch marks. However, if you're gaining weight as you do Bikram, you could still end up with stretch marks, though the stretch marks will not be caused by the yoga.