This study looks at whether a cream containing 10% cholesterol works better than a cream containing 10% urea for people with autosomal recessive congenital ichthyosis (ARCI), a rare inherited skin condition that causes dry, thickened, scaly skin from birth.

People with ARCI have a weakened skin barrier because their skin cannot properly produce or arrange the natural fats (lipids) needed to keep moisture in and irritants out. This leads to excessive water loss through the skin, dryness, itching, cracking, and a higher risk of skin infections. The current standard treatment is urea cream, which helps soften and remove scale but does not repair the underlying fat structure of the skin barrier. Cholesterol is one of the key natural fats that makes up a healthy skin barrier, so applying it directly to the skin may help rebuild that barrier more effectively than urea.

In this study, each participant will have one cream applied to one side of the body and the other cream applied to the matching area on the opposite side, so that each person acts as their own comparison. Researchers will measure how much water the skin loses (transepidermal water loss), skin hydration, and skin pH before and after treatment. They will also assess dryness and itching, take standardized clinical photographs, and ask participants to complete quality-of-life questionnaires (the Dermatology Life Quality Index, or its children's version, the Children's Dermatology Life Quality Index) as well as a satisfaction questionnaire for each cream.

The goal is to find out whether cholesterol cream restores the skin barrier better than urea cream, reduces dryness and itching more effectively, and leads to a better quality of life for people living with ARCI. The results may help guide more targeted skin care recommendations for this rare genetic condition.

This study is being conducted at the Institute of Dermatology, Bangkok, Thailand, and has been approved by the Institute's Ethics Committee.

Autosomal recessive congenital ichthyosis (ARCI) is a rare group of inherited skin disorders caused by mutations in genes required for normal lipid metabolism and barrier lipid assembly in the stratum corneum. The resulting epidermal barrier dysfunction produces generalized dryness, scaling, elevated transepidermal water loss (TEWL), chronic pruritus, and an increased susceptibility to skin infection. These manifestations begin at or shortly after birth and persist throughout life, with substantial negative effects on physical comfort, sleep, social functioning, and psychological well-being, particularly in children.

Current standard care relies on humectant and keratolytic agents such as 10% urea cream, which improve hydration and assist desquamation but do not address the underlying lipid deficiency responsible for barrier impairment. Cholesterol is a principal lipid component of the lamellar lipid matrix that cements corneocytes together within the stratum corneum. Exogenous application of cholesterol has been proposed as a mechanism-based intervention capable of correcting the disordered lipid lamellae characteristic of ARCI, thereby improving barrier integrity and reducing transepidermal water loss. Prior open-label, half-side comparison work in recessive X-linked ichthyosis demonstrated favorable clinical responses to topical cholesterol compared with urea, although that work did not include objective barrier measurements such as TEWL or validated quality-of-life instruments. Combination cholesterol-lovastatin preparations have also shown reductions in disease severity in ARCI. To date, no study has directly compared 10% cholesterol cream with 10% urea cream in patients with ARCI using both physiological barrier measurements and quality-of-life outcomes.

This investigation uses a prospective, randomized, split-body (intraindividual, half-side) comparison design, in which each participant serves as their own control: one cream is applied to a designated body area while the comparator cream is applied to the contralateral, matched area. This design was selected because ARCI is rare and clinically heterogeneous between individuals, making between-subject comparison less efficient than a within-subject comparison.

The primary objective is to compare the efficacy of 10% cholesterol cream and 10% urea cream in restoring skin barrier function, assessed by TEWL and skin hydration. Secondary objectives include comparison of clinical dryness and pruritus severity, changes in skin surface pH, assessment of quality of life using the Dermatology Life Quality Index (DLQI) or, for pediatric participants, the Children's Dermatology Life Quality Index (CDLQI), evaluation of participant satisfaction with each cream, and documentation of clinical change through standardized clinical photography.

Sample size was calculated using a two-dependent-means (paired t-test) formula based on an expected TEWL difference of 4 g/m²/h between treatments, a standard deviation of 6 g/m²/h, a two-sided significance level of 0.05, and 80% power, yielding a minimum requirement of 18 evaluable participants. To allow for an anticipated dropout or missing-data rate of 25%, the target enrollment was set at 24 participants.

This single-center study is being conducted at the Institute of Dermatology, Bangkok, Thailand, and has received approval from the Institute's Ethics Committee

Inclusion Criteria:

1. Male or female patients aged 7 to 65 years
2. Confirmed diagnosis of Autosomal Recessive Congenital Ichthyosis (ARCI), established by history, family/genetic history, clinical presentation, and/or genetic testing
3. Disease activity stable (not in an acute flare)
4. Thai nationality
5. Receiving care at the Institute of Dermatology
6. Willing and able to provide informed consent (or, for participants under 18, assent with parental/legal guardian consent)

Exclusion Criteria:

1. Presence of any other concurrent skin disease
2. Known history of allergy to any component of the study creams
3. Active skin infection (e.g., herpes zoster, viral, fungal, bacterial, or parasitic infection)
4. History of any malignancy
5. Pregnant (confirmed by positive urine pregnancy test), breastfeeding, or planning pregnancy during the study period