Acupuncture is a form of alternative medicine and a key component of traditional Chinese medicine (TCM) in which thin needles are inserted into the body. because the theories and practices of TCM are not based on scientific knowledge, and it has been characterized as quackery. There is a range of acupuncture variants which originated in different philosophies, and techniques vary depending on the country in which it is performed. It is most often used to attempt pain relief, though it is also recommended by acupuncturists for a wide range of other conditions. Acupuncture is generally used only in combination with other forms of treatment. The conclusions of numerous trials and systematic reviews of acupuncture are inconsistent, which suggests that it is not effective. An overview of Cochrane reviews found that acupuncture is not effective for a wide range of conditions. A systematic review conducted by medical scientists at the Universities of Exeter and Plymouth found little evidence of acupuncture's effectiveness in treating pain. Overall, the evidence suggests that short-term treatment with acupuncture does not produce long-term benefits. Some research results suggest that acupuncture can alleviate some forms of pain, though the majority of research suggests that acupuncture's apparent effects are not caused by the treatment itself. A systematic review concluded that the analgesic effect of acupuncture seemed to lack clinical relevance and could not be clearly distinguished from bias. One meta-analysis found that acupuncture for chronic low back pain was cost-effective as an adjunct to standard care, while a separate systematic review found insufficient evidence for the cost-effectiveness of acupuncture in the treatment of chronic low back pain. Acupuncture is generally safe when done by appropriately trained practitioners using clean needle technique and single-use needles. When properly delivered, it has a low rate of mostly minor adverse effects. Accidents and infections do occur, though, and are associated with neglect on the part of the practitioner, particularly in the application of sterile techniques. A review conducted in 2013 stated that reports of infection transmission increased significantly in the preceding decade. The most frequently reported adverse events were pneumothorax and infections. Since serious adverse events continue to be reported, it is recommended that acupuncturists be trained sufficiently to reduce the risk. Scientific investigation has not found any histological or physiological evidence for traditional Chinese concepts such as qi, meridians, and acupuncture points, and many modern practitioners no longer support the existence of life force energy (qi) or meridians, which was a major part of early belief systems. Acupuncture is believed to have originated around 100 BC in China, around the time The Yellow Emperor's Classic of Internal Medicine (Huangdi Neijing) was published, though some experts suggest it could have been practiced earlier. Over time, conflicting claims and belief systems emerged about the effect of lunar, celestial and earthly cycles, yin and yang energies, and a body's "rhythm" on the effectiveness of treatment. Acupuncture fluctuated in popularity in China due to changes in the country's political leadership and the preferential use of rationalism or Western medicine. Acupuncture spread first to Korea in the 6th century AD, then to Japan through medical missionaries, and then to Europe, beginning with France. In the 20th century, as it spread to the United States and Western countries, spiritual elements of acupuncture that conflict with Western beliefs were sometimes abandoned in favor of simply tapping needles into acupuncture points.