affects of sun when using cream

I have been given antibiotics and a cream for my acne and I am not meant to let my face get in contact with the sun, does anyone know why ?

[loiloi]

Hi.
Use of topical retinoids increase your risk of severe sunburn. Apply your acne cream at night. In the morning wash your face with a soap-free cleanser and apply a day cream or foundation which contains SPF. Avoid direct exposure to UV light; sun, tanning beds and lamps.
Less commonly, oral antibiotics (and some birth control pills prescribed for acne) cause hyperpigmentation of the skin if over-exposed to UV light.
Eloise.