Insurance premiums are based on the risk level of the person. Higher the risk of the applicant, more he/she will pay. Many people are denied standard coverage by insurance companies due to a number of reasons such as medical condition, dangerous occupation, age, obesity and tobacco or alcohol users. But these people are not uninsurable.

Insurance companies place these people in high risk category and buy high risk insurance where they have to pay significantly high premium as compared to ordinary life insurance premiums.
Even if a person is in high risk category, life insurance coverage is necessary. The people who qualify for high risk insurance are those who are in a hazardous profession. Professions that are considered high risk include divers, firefighters, miners etc. People in these professions are at a higher risk of getting injured which makes them difficult to insure.
Life insurance companies may deny coverage to people with heart conditions, cancer, diabetes and high blood pressure. They also check medical history of the applicant’s family. If people with medical conditions are denied coverage they can be hard to insure and can opt for high risk life insurance.
Those who consume alcohol regularly or use drugs or smoke may also be denied coverage. There are always chances of accidents due to usage of drugs and alcohol which makes the users unsuitable for normal life insurance.

People can purchase high-risk life insurance from companies that specialize in this type of coverage. This type of insurance provides lower death benefits as compared to standard life insurance policies. High risk insurance companies use "clinical medical underwriting" instead of outmoded mortality tables that are used by traditional life insurance companies. The high risk insurance policy is expensive but gives people the benefit of buying life insurance when they are not able to buy standard insurance policies.