Penis enlargement, sometimes euphemistically called male enhancement, refers to an assortment of techniques intended to increase the girth, length, or erectile rigidity of the human penis. Procedures range from manual exercises to stretching devices and surgical procedures, with reports of successes and failures around the world. While some techniques are known to be outright hoaxes, others can produce some measure of success. Often, in the advertising of fraudulent products, the distinction between temporary enlargement, i.e. erection, and permanent enlargement is deliberately muddied. Little legitimate scientific research has been done specifically on the subject of non-surgical penile enlargement; existing claims of significant and permanent enlargement are generally anecdotal, unverified by objective research, and can be biased by the interests and emotions of the source. At present, there is no proof of any non-surgical technique that permanently increases either the thickness or length of a normal penis. Some general research has been done regarding the safety and efficacy (or lack thereof) of the ingredients of various pharmaceutical or quasi-pharmaceutical preparations, but thus far, nothing has emerged to cause mainstream medicine to adopt any of them. There are also risks inherent in some of the more invasive procedures, with negative outcomes ranging from the tearing of skin and scarring, to permanent loss of sexual function. Due to the speculative nature of any hope for "improvement", social controversy due to the sexual nature of the topic, and the many known cases of permanent injury involved in the endeavor, many medical professionals are sceptical of the subject, and tend to avoid work in this field. Much of the marketing of commercial penis-enlarging treatments is based on unproven assertions that a larger penis enhances sexual prowess and general attractiveness to potential mates. Enlargement of a normal penis is distinguished from seeking relief from the recognized medical condition of micropenis, where surgery to increase the organ's size is sometimes needed for urinary or sexual purposes. Anxiety about the size of one's penis may be (in extreme cases) a psychological/psychiatric condition best dealt with by qualified medical practitioners.