Safety and Efficacy of ARQ-154 Foam in Adolescent and Adult Subjects With Scalp and Body Psoriasis

Inclusion Criteria: * Participants legally competent to read, write, sign and give informed consent, or, in the case of adolscents, assent with consent of a parent(s) or legal guardian, as required by local laws. * Males and females ages 12 years and older (inclusive) at the time of consent for assent (for adolescents). * Scalp psoriasis with an Investigator Global Assessment of Scalp disease severity (S-IGA) of at least Mild ('2') at Baseline. * A Psoriasis Scalp Severity Index (PSSI) score of at least 6 at Baseline. * A PASI score of at least 2 (excluding the palms and soles) at Baseline. * Clinical diagnosis of psoriasis vulgaris of at least 6 months duration as determined by the Investigator. Stable disease for the past 4 weeks. * Females of childbearing potential (FOCBP) must have a negative serum pregnancy test at Screening (Visit 1) and a negative urine pregnancy test at Baseline (Visit 2). * Females of non-childbearing potential must either be post-menopausal with spontaneous amenorrhea for at least 12 months or have undergone surgical sterilization. * Subjects in good health as judged by the Investigator, based on medical history, physical examination, vital signs, serum chemistry labs, hematology values, and urinalysis. * Subjects are considered reliable and capable of adhering to the Protocol and visit schedule according to the Investigator judgment. Exclusion Criteria: * Subjects who cannot discontinue medications and treatments prior to the Baseline visit and during the study according to Excluded Medications and Treatments. * Planned excessive exposure of treated area(s) to either natural or artificial sunlight, tanning bed or other LED. * Subjects currently taking lithium or antimalarial drugs. * Planned initiation or changes to concomitant medication that could, in the opinion of the Investigator, affect psoriasis vulgaris (e.g. beta blockers, ACE inhibitors). * Current diagnosis of non-plaque forms of psoriasis (e.g., guttate, erythrodermic/exfoliative, palmoplantar only involvement, or pustular psoriasis). Current diagnosis of drug-induced psoriasis. * Subjects with any condition on the treatment area which, in the opinion of the Investigator, could confound efficacy measurements. * Known allergies to excipients in ARQ-154. * Subjects who cannot discontinue the use of strong P-450 cytochrome inhibitors e.g., indinavir, nelfinavir, ritonavir, clarithromycin, itraconazole, ketoconazole, nefazodone, saquinavir, suboxone and telithromycin for two weeks prior to the Baseline visit (Visit 2) and during the study. * Subjects who cannot discontinue the use of strong P-450 cytochrome inducers e.g., efavirenz, nevirapine, glucocorticoids, barbiturates (including phenobarbital), phenytoin, rifampin, and carbamazepine for two weeks prior to the Baseline visit (Visit 2) and during the study. * Subjects with PHQ-8 \>/= 10 or modified PHQ-A \>/= 10 at Screening or Baseline. * Females who are pregnant, wishing to become pregnant during the study, or are breast-feeding. * Subjects with any serious medical condition or laboratory abnormality that would prevent study participation or place the subject at significant risk, as determined by the Investigator. * Subjects with a history of chronic alcohol or drug abuse within 6 months of initiation of the investigational product. * Subjects with a history of a major surgery within 4 weeks prior to Baseline (Visit 2) or has a major surgery planned during the study. * Subjects who are unable to communicate, read or understand the local language, or who display another condition, which in the Investigator's opinion, makes them unsuitable for clinical study participation. * Current or a history of cancer within 5 years with the exception of fully treated skin basal cell carcinoma, cutaneous squamous cell carcinoma or carcinoma in situ of the cervix. * Subjects with active infection that required oral or intravenous administration of antibiotics, antifungal, or antiviral agents within 7 days of Baseline/Day 0. * Subjects who are family members of the clinical study site, clinical study staff, or sponsor, or family members residing in the same household of enrolled subjects.