By Nick Triggle
Health reporter, BBC News
There are over 500,000 people in England with dementia
Dementia patients are being unfairly treated, as many are forced to pay for their care, according to campaigners.
An Alzheimer's Society poll of 2,300 people in England found two thirds of patients paid towards care such as help with washing, eating and dressing.
The charity said this should be free as it was linked to a medical condition, but was often classed as a social care need and therefore means-tested.
The government said dementia was a significant challenge facing society.
An estimated 570,000 people have the condition in England, and the figure is expected to double within 30 years.
The survey, of patients and carers, found a third of people being cared for at home were paying more than £50 a week, while more than half of those in care homes were paying £300.
The Alzheimer's Society estimates that, overall, patients pay £2bn a year in fees that should be picked up by the NHS, and described it as a dementia tax.
The charity said dementia patients were discriminated against in a way other patients, such as those with cancer, would never be.
Alzheimer's Society chief executive Neil Hunt said: "The system is not functioning and the way dementia patients are being treated is unfair.
"As the care is because of a medical condition it should be treated free under the NHS. That is not happening and probably won't if we are being realistic."
The charity has produced its report as the government carries out a consultation ahead of its social care green paper early next year, which is expected to propose a reform of funding.
Currently, anyone with assets of more than £22,250, including property, has to pay for their care.
Similar systems operate in Wales and Northern Ireland, but in Scotland personal care is free.
However, all four nations have been dogged by problems of rationing, with ever more limited packages being offered as councils struggle to keep pace with the ageing population.
'Fair and transparent'
Mr Hunt said he believed people would be willing to contribute towards the cost of their care, but that it should be a fair and transparent system.
He said the charity did not have a recommended model in mind, although many experts favour some sort of basic care guarantee that could be topped up by contributions from the individual.
The Department of Health said its consultation ahead of the green paper on social care funding was aimed at finding a fair solution for "patients and taxpayers".
But a spokeswoman added good quality care was "not just about money, but how services are provided and coordinated" - something which was being addressed by the dementia strategy launched earlier this month.
And she said: "Dementia is now one of the most significant health challenges facing our society."