Although it is likely safe to use sun cream on infants less than six months old, it is just safer to keep them out of the sun. Infants under one year of age should always be kept out of the direct sun, (especially during the peak hours between 10am and 4pm) because their sensitive skin can easily burn. Your first line of defence should be physical protection like long-sleeved tops, pants and a wide brimmed hat. Keep the baby under the shade of an umbrella or stroller that has a canopy as much as possible, and don't ever take a tiny infant outside for too long on a hot day. Their little bodies simply can't tolerate extreme temperatures well.
If you are going to use a sun cream and try find one that is specifically made for babies. A hypo-allergenic and fragrance free sun cream that is in an easily applied form is best. Look for products labelled 'broad-spectrum'. These products will protect against both UVA and UVB rays. You should choose one with a SPF (Sun Protection Factor) of 15 or greater. The SPF indicates the amount of protection against sunburn.
Apply the sunscreen at least thirty minutes before you go out and reapply it every two hours while you are outdoors and be sure to apply enough sun cream to protect your baby. Infant experts estimate that most parents only use about half of the recommended amount of sun cream on their babies, thus giving less protection than they need.
Be sure and use a sun cream even if it looks cloudy outside. Cloud cover won't protect your baby's delicate skin from UV radiation since clouds don't absorb all the rays that can do harm.
And remember that no cream, no matter how high the SPF, can offer 100 per cent protection against the sun.