There are several causes for this and it has to do with the following:
1. The site of the lump (which part of the penis)
2. The size of the lump
3. The duration the lump has been present
4. Whether any deformities are present
The common cause of a lump under the skin with no ulceration is Peyronie's disease. This is a rare condition best diagnosed by a Urologist. However, even a cancer can cause a lump.
It is strongly advise that the person who has this problem to see a Urologist for a consultation and to sort out the diagnosis.
Dr Jimmy Beng,