Chris Shieff, a neurosurgeon and a trustee of brain injury association Headway, says even minor knocks can exacerbate the problems caused by an initial concussion.
"In simple terms, any blow to the head can have unrecognisable consequences, either immediately or if there are repeated minor blows, over a period of time that can cause long-term damage," he said.
"It might be only a minor one that leaves you laid low, so to speak, for longer.
"We now have the ability to recognise smaller injuries earlier and have been able to legitimise concern for those people who do suffer problems on more than one occasion."
Hohaia is the latest rugby player to succumb to the effects of concussions, but experts believe progress is being made.
It is not known if Hohaia is still coming to terms with the psychological effects of the high-profile incident but Dr Andrew Rutherford of the British Psychological Society, who is carrying out research into the effects of head injuries to sportsmen, admits it is still a grey area.
"It sounds logical that having your head battered a number of times and possibly consequences for your brain would have psychological results but it's surprisingly difficult to obtain absolutely clear evidence of this," he said.
"What has been done is an implementation of guidelines for people not to keep playing and risk more head injury, which seems eminently sensible.
"However, it's another question of whether or not there is scientific evidence to support that fully."
- AAP
