There are sunscreen products that do not use a chemical barrier to the
UVA/UVB, but instead use a physical barrier.  The cream goes on as usual, but
the main ingredient is titanium dioxide which scatters and reflects the
sunlight.  This may be a good alternative for mothers concerned about the
chemicals in a regular sunscreen.

Since sunscreens are recommended for children six months and up, I would
imagine that any product that can be applied directly to an infant, can be
used by his/her breastfeeding mom.

Elizabeth