Can cetrimide and ketaconozole shampoo be used alternatively every other day to treat sebbhoeric dermatitis? is it safe? wull it damage my scalp?

It's Ok: It is fine to use them both. I would try to limit how often you wash scalp if you have sebbhorea - there is a fine line between not shampooing enough and doing it too often, both of which can irritate the scalp and cause the condition to flare up. I would suggest if at all possible every other day, so as not to dry out scalp oils too much, especially in the winter months.