A study by charity Asthma UK Scotland found eight out of ten Scots with the condition may not be getting the care they need, while one in five say they have never been shown how to use an inhaler.
According to guidelines, those with the condition should receive a written action plan from their doctor or asthma nurse so they know what steps to take when their symptoms get worse.
The charity says this does not occur in the majority of cases, meaning many sufferers are needlessly exposed to greater risk in the event of a serious asthma attack. Those without an action plan are more than four times more likely to end up in hospital.
Hollie Shirley, from Aberdeen, said she was hospitalised after being turned away by her GP.
She said: "My chest was really bad and I was struggling to breathe. I felt like I'd done a 1000-metre sprint and been given a straw to breathe through. Fortunately my neighbour found me while I was having the attack and drove me to hospital."
The 26-year-old said she had not had a review of the treatment she receives for her condition for two years and medical practitioners assumed she could cope as she has had asthma since birth.
Every year in Scotland nearly 5700 people are hospitalised because of a serious asthma attack, but the report says three-quarters of admissions could be prevented with the right care.
Gordon Brown, national director of Asthma UK Scotland, said: "Standards are in place to give healthcare professionals the information and advice they need to prevent asthma attacks and save lives.
"People with asthma have told us key aspects are routinely neglected and that is increasing their risk of serious asthma attacks."
Dr Iain Small, GP and Regional Development Lead at the Primary Care Respiratory Society UK, said: "Clinical guidelines and national policy are clear about what good quality care looks like, and the respiratory community needs to work with health boards, clinicians and patients to turn this into practice."