Is her skin red and scaly? no, her skin looks normal
how do i prevent dry skin?
I give 30 grams of pellets and a large straw ball daily
Oh you must have added the pics while I was relying earlier, lol. How often are you giving baths? Too frequent dust baths can lead to dry skin. If it's getting dry in the house (like turning on heating because of winter) you may need to offer the dust less frequently. The bald area just looks like a fur slip, it's a defence if they get grabbed or something scares them.
So you are feeding straw not hay? Straw is bedding not food, it has no real nutritional value. You want to be feeding a grass hay, ideally timothy hay. Also is he eating all his pellets everyday? If so and still loosing weight you can try adding more and see if that helps.
I see in one of the pics you have two chins? If so are you feeding each that amount a day? 30 grams is the amount for a single chin, so for two you should be feeding at least 60 grams. Also do you have a bowl for each chin? It's not uncommon for one to hog all the food, it's best to have two of everything, food bowls, water bottles, hay areas, that way one can't eat it all or prevent the other from eating.