A sebaceous cyst or dermoid cyst.Needs surgical removal.
The painless lump that your husband is having seems like a sebaceous cyst. A sebaceous cyst is a closed sac occurring just under the skin which contains a "pasty" or "cheesy" looking substance called keratin.They may occur anywhere on body but scalp, ears, back, face, and upper arm, are common sites for sebaceous cysts. Blocked sebaceous glands, swollen hair follicles and excessive testosterone production will cause such cysts.
Generally no treatment is required but they become painful then it means they are infected,Then surgical excision by traditional wide excision, minimal excision, and punch biopsy excision may be required.
Hope it helps.Take care and pls do keep me posted on how you are doing or if you have any additional doubts.Kind regards.
thank you so much for your intuitive and informative response.