Here's what you need to know about vitamin D, the immune system, skin rashes like eczema, and allergies.

Low vitamin D is linked to increased severity of eczema.
Vitamin D helps inhibit Staphylococcus aureus bacteria. A problem bug for many with eczema.
Vitamin D can speed up healing of the skin barrier, and stabilize the immune function of the gut and skin.
Vitamin D regulates the immune system by encouraging the production of anti-inflammatory chemical messengers, and by blocking the release of inflammatory ones.
Vitamin D cuts down the release of IgE (immunoglobulins present with food and environmental allergies).

And get this, supplementing mom with vitamin D can help colonize the infant gut with important, healthful microbes.

Because gut flora influences the development of eczema and other allergic conditions, supplementing vitamin D in pregnant women and in babies may help reduce these risks in kids!

Get vitamin D levels checked BEFORE supplementing, and work with a knowledgeable practitioner to determine the right dose (for you and your child).

Conventional medicine notes that a level of 30ng/mL is sufficient. From a functional perspective, that is LOW. Optimal levels to shoot for are more likely between 50-75ng/mL.

References

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6518061/
https://athenaeumpub.com/vitamin-d-deficiency-and-its-relation-to-allergic-diseases-a-cross-sectional-study-among-allergic-patients-from-jeddah-city-saudi-arabia/