Soft, breathable organic cotton infant socks are the best starting point for sensitive skin, for the same reasons organic cotton works well across the rest of the wardrobe: it is grown without the pesticides and harsh chemical treatments used in some conventional cotton production, and it tends to feel gentler against skin that reacts easily.
Look for socks with flat, minimal seams, particularly around the toe, since a bulky seam is one of the most common sources of irritation in baby socks, especially for babies who spend a lot of time barefoot-adjacent in soft-soled shoes.
Avoiding tight elastic at the cuff also matters for sensitive skin, since a sock that grips too hard can leave marks or cause irritation over a full day of wear, even if the fabric itself is soft. A snug but gentle cuff strikes the right balance between staying on and staying comfortable.
If your baby has particularly reactive skin or eczema, cotton socks for newborn sizes in a simple, undyed or lightly dyed style are generally the safest choice, since heavier dyes and prints can occasionally contribute to irritation on already sensitive skin.