Treatment adherence remains a major challenge to effectively managing scalp psoriasis. Several studies reported that between 39% and 73% of patients do not follow their prescribed topical psoriasis regimen [34] and nearly 50% of topical prescriptions for dermatological conditions are not being filled [35]. In this context, CAL/BDP PAD-cream represents a promising formulation for promoting adherence, thereby improving treatment outcomes and patient satisfaction [20, 22]. To evaluate how adherence influences treatment success, we conducted a subgroup analysis of PROs, ClinROs, and treatment preferences among 252 PRO-SCALP participants with varying adherence levels.

Based on VAS classification, 59.9% of patients demonstrated high adherence, consistent with an online survey in which 66% of patients with plaque psoriasis reported high adherence to CAL/BDP PAD-cream [36]. Different characteristics likely contribute to this pattern. Treatment complexity and perceived convenience strongly influence adherence [37], and CAL/BDP formulations support this through once-daily dosing [34, 38]. Indeed, adherence to once-daily CAL/BDP therapy was nearly double that for twice-daily therapies [39]. The choice of vehicle is also key for maximizing adherence, as cosmetic acceptability affects willingness to use topical treatments. In a study comparing different vehicles, patients with scalp psoriasis preferred gel and cream over ointment, which was perceived as greasier, slower to apply, and more difficult to use [40]. Although creams can be less acceptable than gels as a result of their lipophilic nature, the PAD technology confers CAL/BDP PAD-cream favorable sensory characteristics [41] offering greater convenience than the gel and faster onset of action, while achieving higher PGA success rates and greater improvements in mPASI and QoL [20]. Moreover, CAL/BDP PAD-cream demonstrated increasing efficacy with greater disease severity, unlike the gel formulation [20].

Treatment satisfaction is critical for supporting adherence. In our study, patients with high adherence reported significantly greater scores in the Convenience domain of the TSQM-9 questionnaire, and Overall Satisfaction compared with patients with low adherence. In contrast, both adherence subgroups reported similarly high satisfaction with the effectiveness of CAL/BDP PAD-cream, indicating that perceived effectiveness was not fully dependent on adherence level. However, the consistently positive direction of the effect estimates may indicate clinically meaningful trends that could be confirmed in larger or longer-term studies. In parallel, high adherence was also strongly associated with higher treatment preference and usability scores, indicating that patients with high adherence tended to prefer CAL/BDP PAD-cream over their previous treatments, which may explain the greater number of tubes used. Overall, patients with high adherence exhibited greater satisfaction, preference, and usability with CAL/BDP PAD-cream, revealing stronger cosmetic acceptability.

Patients with high adherence achieved the greatest clinical effectiveness, showing greater reductions in itch severity and scalp psoriatic lesions at week 8 than patients with low adherence. Adherence demonstrated strong associations with changes in S-mPASI and WI-NRS scores over time. The significant interaction observed suggests that the beneficial effect of adherence strengthened over time, particularly by week 8, supporting the importance of sustained adherence throughout treatment. Nonetheless, patients with low adherence also experienced significant improvements in these outcomes and achieved scalp-PGA success rates comparable to those with high adherence. Hence, although CAL/BDP PAD-cream’s potency and patient-centered design allow meaningful improvements even with lower adherence, high adherence is consistently associated with greater clinical improvements in itch severity and overall skin restoration.

Despite the improved patient outcomes in scalp psoriasis, only 60% of patients achieved high adherence. The full analysis of PRO-SCALP showed that 54.2% discontinued treatment once symptoms improved [22]. Also, although most patients (70%) reported no difficulty in remembering their treatment, nearly half (48.2%) admitted forgetting doses, showing that forgetfulness remains a main barrier to adherence [22]. Consequently, since adherence to topical therapy is influenced by various factors beyond the medication itself [39], strategies such as reminder text messages, educational sessions, a good physician–patient communication, and addressing comorbidities and predisposition factors, may be necessary to further favor adherence [42,43,44,45].

Scalp psoriasis has not only physical but also psychological and emotional implications. Phase 3 trials and prospective studies have shown that CAL/BDP PAD-cream significantly reduces the impact of psoriasis on daily activities, personal relationships, and self-esteem [22, 46]. In our study, patients with high adherence experienced fewer symptom-related QoL impairments and greater psychosocial benefits than patients with low adherence, further highlighting the role of adherence in reducing symptom burden. The significant interaction between adherence and Scalpdex Symptoms score at week 8 evidence an increased influence of adherence over time. In contrast, the association with remaining Scalpdex domains was not significant, which may reflect variability in subjective perceptions, or a longer timeframe needed for patients to report emotional and functional improvements. Overall, although CAL/BDP PAD-cream provides meaningful benefits regardless of adherence level, improvements tend to be smaller and sometimes less durable among patients with low adherence [12, 47]. These improved QoL outcomes likely stem from the greater reductions in itch and visible lesions seen in the high-adherence subgroup [48]. Studies then describe a positive feedback loop in which better QoL and psychosocial well-being increase motivation and treatment satisfaction, further reinforcing adherence in return [47].

Improvements in sleep quality have consistently been reported with CAL/BDP psoriasis therapy, in line with our findings, as sleep commonly improves when skin inflammation decreases [49]. Yet, sleep quality did not show additional improvements with higher adherence. This pattern aligns with findings from clinical trials and real-world studies, which show that sleep quality tends to improve alongside other outcomes but may plateau in patients with high adherence levels [46, 50, 51]. One possible explanation is a threshold effect, whereby once disease-related discomfort has been reduced beyond a certain point, further improvements in sleep may require intervention in other factors (e.g., distress, comorbidities, habits) [46, 50, 51]. Nevertheless, this interpretation should be viewed cautiously, as sleep outcomes may be influenced by multiple factors beyond psoriasis-related discomfort.

Both adherence subgroups showed broadly similar baseline demographic characteristics. Previous studies have reported that men are significantly less adherent to topical therapies than women [39, 52], although other investigations have found poorer adherence among women [53], or no gender differences at all [54]. However, no studies specifically evaluated scalp psoriasis. Because our study did not include head-to-head comparisons, no conclusions can be drawn on the influence of these demographic variables on CAL/BDP PAD-cream adherence. Notably, patients with high adherence tended to report greater baseline scalp itch severity, as reflected by significantly higher baseline Scalp WI-NRS scores than those with lower adherence (6.9 vs. 5.8, respectively, p value = 0.0003). Similarly, patients with moderate disease at baseline according to the Scalp PGA reported higher adherence at EOS than those with mild severity, although we hypothesize this pattern may be reversed among individuals with severe disease. Prior evidence has suggested the opposite relationship, with greater disease severity associated with poorer adherence, possibly due to frustration with previous treatment failures [39]. Nevertheless, both adherence categories showed a statistically significant reduction in WI-NRS from baseline to EOS, decreasing from 6.9 to 2.5 in patients with high adherence and from 5.8 to 3 in patients with low adherence (p < 0.0001 for both categories), indicating that clinically meaningful symptom improvement occurred across adherence groups despite the baseline imbalance. Finally, older patients demonstrated greater adherence in our study, which may reflect more experience managing flare-ups. This aligns with evidence showing that younger patients tend to have lower adherence than adults [55]. Overall, adherence to scalp psoriasis treatment appears to be influenced by a combination of disease-related and individual factors.

This study presents some limitations. Although the mixed-effect models may have largely accounted for the observed imbalance in baseline disease severity between adherence groups, we cannot exclude the possibility that this imbalance influenced the estimation of CAL/BPD PAD-cream effectiveness to some extent. An additional limitation in this study relates to the selection of the cut-points used to derive categorical adherence variables. Although the 80% threshold is widely used in the adherence literature to distinguish high from low adherence across chronic diseases from several therapeutic areas, including dermatology, this cut-point remains to some extent conventional rather than disease-specific [45]. As a result, the use of alternative cut-points may have yielded different adherence distributions and, consequently, different effect estimates.

Overall, this study demonstrates that high adherence to CAL/BDP PAD-cream has a direct positive impact on scalp psoriasis outcomes, resulting in improved clinical effectiveness, QoL, and patient satisfaction, while patients with low adherence experience meaningful, though smaller, benefits. These strong results in patients with high adherence may, in turn, reinforce continued adherence and support long-term disease control, underscoring the need for targeted efforts to promote adherence in a broader proportion of patients.