Blow driers have become quite a convenience and can be safe if used properly. The most common error in the use of these tools is continuing to apply high heat to hair that is already dry.
Moist hair is capable of absorbing a surprising amount of heat, which converts the moisture to water vapor and carries it away from the hair. But once the hair has become dry, the heat has no place to go and just builds up in the hair, which can damage it.
When using a blow drier, be sure to monitor the moistness of your hair, so you can be sure that excessive heat won’t be applied to hair that is already dry. And use a heat protector before you begin to blow dry your hair. Like this one: