People who have alopecia should be allowed one human hair wig per year on the NHS in England, a charity says.
At the moment, local health bosses decide how many wigs patients are entitled to in their area.
Alopecia UK says its data suggests in some areas patients are offered two wigs a year, while in others they aren't offered any.
NHS England said there is no nationally set limit and "all patients' needs and circumstances are different".
Jen Chambers, the charity's development manager, says there should be consistency.
"Some people literally will not leave their house without hair on their head.
"So if we want people with alopecia to contribute to society then there should be help there for all those who need it."
Alopecia is the scientific term for hair loss and is estimated to affect at least 65,000 people in the UK.
In younger people it is thought to often, though not always, be caused by an auto-immune condition.
In 2015, Alopecia UK sent freedom of information requests to the 209 Clinical Commissioning Groups (CCGs) in England asking about wig provision in their area.
Of the 169 that got back to them - six said they don't offer wigs because they view alopecia as a "cosmetic issue".
The other responses varied. Some groups said they offered two wigs a year as standard, while others said it was decided on a case-by-case basis.
Twenty five NHS groups referred to NHS England's policy.
It states: "There are no nationally set limits on the number of wigs a patient can have on the NHS, but there's nothing preventing local NHS organisations from setting their own limit."
Greg Burnet, who's 26, completely lost his hair when he was 13.
"I scratched my head in music class and some hair came out and I remember the girl next to me being like 'What the hell?'
"It was an overnight thing," he says.
Despite seeing multiple doctors, dermatologists and specialists over the years, no-one has ever offered to prescribe him a wig.
"I would've been a different person. The alopecia has completely changed me and if I had an option of a wig it might not have done.
"Whether it's for better or worse - I wasn't given a choice and that's not fair."
Human hair wigs can cost several hundred pounds and the charity says it's heard from people who've had to cut back on essentials just to afford theirs.
Jen, who has alopecia herself, used to get real hair wigs prescribed to her on the NHS - but in recent years she says the service has been cut.
"I remember when they told me - I just couldn't hold it together and I burst into tears," she says.
The British Association of Dermatologists has echoed the call for a consistent NHS wig policy.
"Wig provision should be equal across the NHS, regardless of where you live.
"Alopecia can have an enormous impact on quality of life and should not be considered a cosmetic issue."
An NHS England spokesperson said: "It's important to be clear that there is no nationally set limit and all patients' needs and circumstances are different, and local GP groups who make these decisions take this into account."