4 weeks post op, can I use sunscreen on scars or could this potentially cause infection?

Silicon-based scar creams are the most recommended topical cream to use at this point in time, assuming you are healing without complications. Sunscreens are good to use after the wounds have closed and there is little risk of developing an infection. Consult with your surgeon regarding this as each surgeon has his/her own protocols to follow.

Thank you for your question.  I generally recommend that my patients begin using silicone-based scar gel with SPF 2-3 weeks after most surgeries assuming the wound are healing well.  If the wounds are closed, there is no contra-indication to using sunscreen or topical moisturizers.  Topical antibiotics such as bacitracin are not necessary and can cause an allergic response with prolonged use.  Good luck!