Inclusion Criteria:  Ages 18 years and older Primary DSM-5 diagnosis of obsessive-compulsive disorder Mild to Moderate OCD severity (8 ≤ Y-BOCS ≤ 23) Subjects must currently be engaged (initiated and ongoing) in formal psychotherapy, ERP, prior to enrollment Subjects currently on medication that wish to participate in the study: Taking a confirmed adequate and stable dose of a Serotonin Reuptake Inhibitor (SRI) or Selective Serotonin Reuptake Inhibitor (SSRI), as determined by the Investigator, for at least 6 consecutive weeks prior to screening Confirmed contamination fears, as defined by a score of at least 10 points on the Padua Inventory Contamination Fear Subscale 30 (PI CF) during the initial telephone screening and at least 9 on the PI CF during the first laboratory testing session CGI-Severity score ≥ 2 Currently living in the United States Ability to read, write, and comprehend English Patient willing to provide informed consent  Exclusion Criteria:  Subjects who are study site staff members or subjects who are employees directly involved in the conduct of the study Subjects with a history of at least two (2) treatment failures with a Serotonin Reuptake Inhibitor (SRI) and/or Selective Serotonin Reuptake Inhibitor (SSRI) at a confirmed adequate dose and for an adequate duration, as determined by the investigator Severe and extreme OCD severity (Y-BOCS ≥ 24) Current or previous symptoms of psychosis, including delusions, or history consistent with a psychotic disorder, in the opinion of the investigator Current or previous compulsions that may place the subject or others at risk, in the opinion of the Investigator History of a violent tendencies, action(s) or thoughts or predilection towards violence in the opinion of the Investigator Any comorbid diseases or disorders (as determined by clinical judgement and supported by the MINI v.6 diagnostic instrument) that significantly elevates the risk of study participation or obscure the evaluation of effectiveness (e.g., psychotic disorders, Major Depressive Disorder, Bipolar Disorder, evidence of dementia or other Cognitive Disorder) Baseline C-SSRS: answer of yes to items 3, 4 or 5 within previous 12-month period) and/or BDI-II Exclusion (item 9, score of 2 or 3) History of one or more suicide attempts (in the last 12 months) or subjects who, in the opinion of the investigator, present a serious risk of suicide, determined also by C-SSRS Subjects presenting a risk for self-harm or self-injurious behavior(s) or a risk of harming others (in the last 12 months) as judged by the investigator in consultation with the medical monitor Current severe substance use disorder as determined by the M.I.N.I diagnostic instrument excluding caffeine Vision or hearing impairment that, in the opinion of the Investigator, might reduce, limit or adversely affect the subject's ability to comply with the requirements of the study or might affect the integrity of the data Does not own a supported mobile smartphone with a data plan Any physical, medical (including psychiatric) or other condition that, in the opinion of the investigator, might reduce, limit or adversely affect the subject's ability to comply with the requirements of the study or might affect the integrity of the data Use of a smartphone app in past for treatment of any psychiatric disorder, including OCD, depression or anxiety disorder A history of addiction to, dependence on, abuse of, misuse of, distribution of or use of any substance, including alcohol and nicotine, within the past one year