As a nursing mother, it's important to be cautious about the skincare products you use. Niacinamide, a form of vitamin B3, is generally considered safe and is commonly used in topical skincare products like serums. It has anti-inflammatory properties and is unlikely to harm you or your baby when applied to the skin.

However, since your body is in a sensitive state during breastfeeding, it's always best to:

• Check the full ingredient list of the Plums niacinamide serum to ensure there are no other potentially harmful ingredients.
• Avoid products with strong fragrances, alcohol, or other irritants that might affect your skin or your baby.
• Consult your healthcare provider or a dermatologist to confirm that this specific product is safe for your use during nursing.

In general, topical niacinamide is low risk, but personalized advice is always the safest approach during breastfeeding.