This topic has long been an issue for my Alex, and has also piqued my "need to know" gene, so I have spent some time poking around the Oncology medical journals and websites for healthcare professionals(I am highly skeptical of other sources). There is an awful lot out there and many theories about the hows and whys of what is going on. I am confident this information is credible BUT there may be inaccuracies as a result of my own misinterpretation of the information (please correct me if you know what I am trying to say but haven't got it right).

Before I share what I have learnt, some definitions:
- hypo - means less of
- a - means lack of
- dys - means disturbance or not normal
- osmia- refers to sense of smell
- geusia - refers to sense of taste

So dysgeusia is disturbance of sense of taste whilst hyposmia means reduction in sense of smell.

The literature struggles to disentangle taste and smell as the pair are interrelated to the point that if one is impaired the other is affected and it is difficult to pinpoint which is impaired to affect the other.

Chemotherapy causes smell and taste disturbances - particularly absent and "wrong" sense of taste and smell. The two culprits relevant to this forum are 5FU and cisplatin. Although I do not recall reading about carboplatin specifically, I would be unsurprised if it too were implicated in some way.

Depending on the trial, 50-80% of patients suffer smell and taste disturbance after chemotherapy. The chemotherapy refers to multiple combinations of chemo agents used as regimen over 9-12 weeks rather than a single agent administered in conjunction with radiation to make the radiation more effective.

There are many suggested mechanisms including
a)direct insult to salivary system - chemo is secreted in the mucous, giving everything a metallic taste.
b)neurotoxicity - chemo damages the nerve system responsible for taste and smell.
c)side effects - chemo causes stomatitis (inflammation and ulceration) and xerostomia (dry mouth due to lack of saliva)which in turn causes dysgeusia and dysosmia.
d)chemo is effective in killing cells that have a high turnover and taste buds have a high turnover rate. One would expect lack of or absent taste bud would result in reduction of ability to taste.
e)chemo causes deficiencies in vitamins and minerals such as zinc which interferes with appetite and taste

We all know that radiation causes dry mouth and ulcers and this would be one of the reasons why radiation is also implicated in the smell and taste disturbances. It also "nukes" taste buds and damages nerves so the outcomes of b) and d) could also be attributed to radiation.

I couldn't find anything about the concept of "heightened smell". Maybe when taste buds and olfactory system regenerate and the nerves recover, it is like the smell of the world after the rain - everything has been washed clean and you get to start again with a fresh set of senses???