It is known that intensive tanning may be the cause of cancer. Despite this knowledge, some people have excessive tanning habits. Researchers pointed out an addictive behavior behind this habit.
One Study found that both problematic tanning and dependence were significantly associated with being female and with higher scores on screening measures of obsessive-compulsive and body dysmorphic disorders. Frequency of use in the past month was the strongest correlate of problematic tanning (p < .001) and dependence when included in a model that controlled for shared variance among demographics and psychopathology.
A metastudy was conducted using PubMed and Google Scholar and using the following key words alone or in combination: tanning, addiction, dependence, tanning bed, sun exposure, and solarium. It 41 English-language articles from 1974 to 2013. It showed many excessive indoor tanners meet symptom criteria adapted from the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) substance abuse and dependence criteria. Trial studies suggest that there may be a physiological basis, consisting of dependence on opioids, for excessive indoor tanning behaviors. It can be included in the spectrum of addictive behaviors, although other models may be proposed. Further controlled studies must be performed, especially in neurobiology and imaging, to improve our understanding of tanning dependence. 
Study finds correlation between exzessiv tanning, substance abuse and anxiety
To assess tanning-related characteristics, psychopathology, and demographics, the researchers administered questionnaires to 533 tanning university students; 31% met criteria for dependence, 12% for problematic use. Results suggest that many who engage in excessive tanning may also have significant psychiatric distress. Additional research is needed to characterize compulsive, problematic use and its rates, correlates, and risk factors among diverse samples. 
Diagnostic instrument Behavioral Addiction Indoor Tanning Screener (BAITS)
A pretty new Study from 2017 tested the validity and reliability of the BAITS by using a multi-method approach.
It used data from the first wave of the National Cancer Aid Monitoring on Sunbed Use (NCAM), which includes a cognitive pretest (08/2015) and a Germany-wide representative survey (10-12/2015). In the cognitive pretest 10 participants were interviewed, while 3,000 individuals aged 14 to 45 years were included in the representative survey. Potential symptoms of indoor tanning addiction were measured via the BAITS, a brief screening survey including seven items (answer categories: yes vs. no). Criterion validity was assessed by comparing the results of BAITS with usage parameters. Additionally, we tested internal consistency and construct validity. 19.7% of current and 1.8% of former indoor tanning users were screened positive for symptoms of a potential addiction. The research found associations between usage parameters and the BAITS (criterion validity). Compared to other short instruments measuring symptoms of a potential addiction, the BAITS seems to be a valid and reliable tool.