however can also be pleasurable and may be self-imposed thus blurring the distinction to recreation. Many activities in entertainment are work for one person and recreation for another. Over time, a recreational activity may become work, and vice versa. Thus, for a musician, playing an instrument may be at one time a profession, and at another a recreation. Similarly, it may be difficult to separate education from recreation as in the case of recreational mathematics. Health and recreation Recreation has many health benefits, and, accordingly, Therapeutic Recreation has been developed to take advantage of this effect. The National Council for Therapeutic Recreation Certification (NCTRC) is the nationally recognized credentialing organization for the profession of Therapeutic Recreation. Professionals in the field of Therapeutic Recreation who are certified by the NCTRC are called "Certified Therapeutic Recreation Specialists". The job title "Recreation Therapist" is identified in the U.S. Dept of Labor's Occupation Outlook. Such therapy is applied in rehabilitation, psychiatric facilities for youth and adults, and in the care of the elderly, the disabled, or people with chronic diseases. Recreational physical activity is important to reduce obesity, and the risk of osteoporosis and of cancer, most significantly in men that of colon and prostate, and in women that of the breast; however, not all malignancies are reduced as outdoor recreation has been linked to a higher risk of melanoma. Extreme adventure recreation naturally carries its own hazards. Forms and activities Recreation is an essential part of human life and finds many different forms which are shaped naturally by individual interests but also by the surrounding social construction. Recreational activities can be communal or solitary, active or passive, outdoors or indoors, healthy or harmful, and useful for society or detrimental. Some recreational activities – such as gambling, recreational drug use, or delinquent activities – may violate societal norms and laws. A list of typical activities could be almost endless Hobby A significant section of recreational activities are designated as hobbies which are activities done for pleasure on a regular basis. A hobby is considered to be a regular activity that is done for enjoyment, typically during one's leisure time, not professionally and not for pay. Hobbies include collecting themed items and objects, engaging in creative and artistic pursuits, playing sports, or pursuing other amusements. Participation in hobbies encourages acquiring substantial skills and knowledge in that area. A list of hobbies changes with renewed interests