The following is a follow up to a questioned I Answered for @wildwildwasteland.
In Fallout I have always been fascinated by the lore. So I always read every source I could in game. Especially terminals.
The following is based on that and on the official wiki.
Ghouls in Fallout are largely based on what the 1950s knew about radiation and belived would occur go humans. Such as mutations (which we see in pre-war depictions of Vault Boy being irritated. He grows am extra appendage).
In Fallout when a Human is exposed to large amounts of radiation they are rapidly mutated into a ghoul. Mostly only really die from other factors. Such as physical damage to the body like a Nuclear heat blast or debris. Which is why most ghouls come from humans that were exposed to radiation who were protected from physical damage somehow. Like those in Necropolis (A Failed Vault) or were in the metro system taking shelter). And most new ghouls come from exploring irradiate places. However not everyone becomes a ghoul. It appears to be largely triggered by your own actions like taking radaway and radx whilst still being irradiated or consuming irradiated food. Slowly exposing your body to radiation. By our science of today we know that such things would cause thyroid or stomach cancer.)
Ghouls differ from us mostly because their DNA has been altered. It regenerates faster and gives them their long lives. Making them resistant to disease, injury and death. Radiation even heals them.
Physically they resemble zombies. Their ears and nose are long gone because ghoulification means soft tissues fall apart such as cartilage and tendons. Which is why ghouls experience arthritic pain in their joints. Their skin is flaking and falling off due to it dying. But because of their regenerative properties they have what one could argue as a type of psoriasis. Whilst not an immune disorder this type is purely because their DNA and bodies are regenerating and repairing at such a rate that their skin is continuously flaking.
The damage to soft tissue is also why they have such rough voices. The larynx is damaged.
Realistically female ghouls should be fairly flat chested and the males would lack genitalia bulges. The penis and memory glands would of degenerated. However it can be argued that due to the regenerative properties these organs and tissues remain largely intact.
There is a downside. Due to the process they can be time bombs. Eventually the brain degenerates over time. Turning them feral. This has largely been insinuated to be due to some form of brain damage or trauma. Such as a blow to the head or preexisting damage prior to ghoulification.
Many ghouls live long productive lives and don’t become feral. Others do. Radiation exposure can accelerate the process. Suggesting that ghouls living in places with higher rad counts are more likely to become feral. And it suggests that while radiation heals them it still has ionising effects on brain tissue and nurons.
I hope any of my followers find this helpful. If you notice mistakes then by all means please feel free to reblog and add your comments. I welcome all to a good discussion on the science of fallout.
But bare in mind that the theory of ghouls being a product of the FEV and Radiation is no longer considered canon.