Maximal Usage Pharmacokinetics and Safety Study of ARQ-154 Foam 0.3% in Pediatric Participants With Scalp and Body Psoriasis

Who May Qualify: - Males and females, ages 2 years to \< 12 years old at Day 1. - Clinical diagnosis of psoriasis vulgaris of at least 2 months duration at Screening as determined by the Investigator. - Scalp psoriasis with an Investigator Global Assessment (S-IGA) of scalp disease severity of at least Moderate ('3') at Day 1. - An IGA of body (non-scalp) psoriasis (B-IGA) of at least Mild ('2') at Day 1. - Extent of scalp psoriasis involving ≥ 10% of the total scalp at Day 1. - Body psoriasis (non-scalp) involving at least 3% BSA on Day 1. Who Should NOT Join This Trial: - Participants who cannot discontinue medications and treatments prior to Day 1 (first application of IP). - Current diagnosis of non-plaque forms of psoriasis. Current diagnosis of drug-induced psoriasis. - Participants who have significant active systemic or localized infection or have had any infection that required oral or intravenous administration of antibiotics, antifungal or antiviral agents within 7 days prior to Day 1. - Participants with skin conditions other than psoriasis vulgaris that would interfere with evaluations of the effect of the study medication, as determined by the Investigator. - Participants who cannot discontinue the use of strong cytochrome P-450 CYP3A4 inhibitors for 2 weeks prior to Day 1 and during the study period. - A medical history of severe renal insufficiency, moderate to severe hepatic disorders (e.g., Child-Pugh B or C), or chronic infectious disease (e.g., hepatitis B, hepatitis C, or human weakened immune system virus \[HIV\]). - Participants who are family members of the clinical study staff or sponsor. Always talk to your doctor about whether this trial is right for you.