[energizer21_200]

I have four chickens and they are all losing their feathers on their underside. They a been like this a couple of months now. They are treated for red mite and lice every month and give Verm-x, and fed a well balanced diet. I never see them pecking eack other. Does anyone know what is causing it, or is it part of molting?

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[joyfull]

How are you treating them for redmite? redmite live in the coop and only feed on the chickens overnight - they then return to hide in the nooks and crannies inside the coop or under the roofing felt.
Why are you using Verm-X? if it is to stop or eradicate worms then please change onto using Flubenvet - this is proven to get rid of worms whereas verm-x has no written proof (despite lots of people writing to them asking for scientific proof).
Do your bald hens perch overnight or sleep in the nest box or on the floor? If they sleep on the floor or in the nest box then they will be sleeping in pooh which will burn the feathers and skin especially if it isn't removed daily - they also run the risk of getting infections.
Do your hens spend a lot of their time in the nest box? in which case they could be broody and they lose their feathers so that they can warm the eggs with their body heat.

just going to move this post over to the hen house so you may get more responses to your problem 

[energizer21_200]

Thanks for the reply. I treat them for redmite by spraying the birds with Johnsons anti-mite extra every three weeks, and i spray the coop every couple of months with poultry shield concentrate. I've been using Verm-x just as a precaution. The hens perch overnight, and they only use the nest box for laying.