The goal of this clinical trial is to demonstrate the feasibility of a trial that examines the impact of changes in dietary sodium intake on skin sodium levels, atopic dermatitis, and psoriasis. In addition, it aims to generate preliminary data to begin to answer the following questions:

1. Is there an association between skin sodium concentration and atopic dermatitis and psoriasis severity?
2. Are changes in dietary sodium are associated with changes in skin sodium concentration and atopic dermatitis and psoriasis severity?

Researchers will compare sodium tablets to a placebo (a look-alike substance that contains no drug) to specifically examine the impact of altering sodium intake.

Participants will:

• Follow a low-salt diet for the duration of the 13-week study
• Take sodium chloride tablets every day for 5 weeks followed by a placebo every day for 5 weeks after a 2-week washout period, or vice versa
• Visit the clinic up to 4 times to answer questionnaires, provide bio samples, complete dietary recalls, and undergo non-contrast sodium MRI

The central hypothesis of this proposal is that excess dietary sodium (consumed primarily as salt) is concentrated in the skin as a physiologic response to poor barrier function, and that a low-sodium diet can improve inflammatory skin disease severity. This study is meant to generate pilot data to complement the iDOSE trial (NCT07447063). The study will recruit 50 individuals (10 participants with atopic dermatitis, 10 with psoriasis, and up to 30 'healthy' individuals without skin disease) and measure skin sodium concentration using a non-invasive sodium MRI technique. Healthy individuals will only undergo sodium scans at Visit 1. Participants with atopic dermatitis and psoriasis will be counseled on how to follow the DASH low-sodium diet and asked to maintain the diet for the duration of the 13-week study. After a 1-week wash-in period on the diet alone, they will be asked to add daily sodium chloride tablets in a self-controlled cross-over design. Participants will be randomized in equal groups to either start with sodium tables or placebo tablets. One group will receive sodium tablets for weeks 2-6, no tablets for a washout period during weeks 7-8, then placebo tablets for weeks 9-13. The other group will receive placebo tablets for weeks 2-6, no tablets for a washout period during weeks 6-8 then sodium tablets for weeks 8-13. Sodium consumption will be evaluated using dietary recall questionnaires and urine biomarkers and eczema and psoriasis activity and severity will be measured using validated severity scores and patient-reported outcomes.

Inclusion Criteria:

• Participants ages 18 years
• Willing and able to undergo non-contrast MRI.

Exclusion Criteria:

• Contraindications to MRI (such as cardiac pacemakers, claustrophobia, non-compatible intracranial vascular clips, IUDs, or other implants)
• A cardiac event in the past 6 months
• Impaired function of the liver or kidney (glomerular filtration rate <60 mL/min)
• Medications that influence sodium excretion (e.g., diuretics or SGLT2 inhibitors)
• Antibiotic or immunomodulatory medications within the last month
• Contraindications to sodium tablets

(Topical medications used exclusively on the head/neck or hands/feet (e.g., antifungal nail treatment, antidandruff shampoo, acne cleansers) are acceptable. Topical and systemic eczema treatments are acceptable if the participant has been on a stable dose for at least 2 months and still meets the severity entry criteria. Patients on dupilumab will not be excluded if they have been on dupilumab for at least two months and still meet the disease severity inclusion criteria.)

All IPD that underlie the results in a publication

Beginning 1 year and ending 5 years after publication of the results

Researchers interested in accessing data from the project must submit a written resource request via email to the Principal Investigator and sign a Data Use Agreement. De-identified data will be shared through a secure server.

Clinical research coordinators will be masked.