Overview: Before you can understand specific policy types, you need to know what health insurance is actually insuring against — the underlying perils and categories of loss the industry is built around.

Health and accident insurance is designed to protect policyholders against the financial consequences of two fundamental perils: accident and sickness. In insurance, a peril is the cause of a loss — the event that triggers the policy. Every health insurance claim traces back to one of these two origins, and understanding the distinction matters because policies often treat them differently.

An accident is defined as a sudden, unexpected, and unintentional external event that causes bodily injury. The key words are "sudden" and "external" — the event comes from outside the body and happens without warning. A fall down a staircase, a car collision, and a workplace machinery injury are all accidents. By contrast, a sickness is an internal condition — an illness or disease that develops within the body, even if symptoms appear suddenly. Pneumonia, cancer, diabetes, and appendicitis are all sicknesses, regardless of how quickly they progress. The line between the two matters for claim eligibility: an accident-only policy pays nothing for pneumonia, and some disability policies pay benefits for different durations depending on whether the disability stems from an accident or a sickness.

The distinction also affects waiting periods. Coverage for accidents typically begins immediately — there is no way to anticipate an accident, so there is no reason to delay coverage. Sickness coverage, however, often carries a short probationary period (commonly 30 days) to discourage people from buying coverage only after they notice symptoms. This is a basic adverse selection control.

The Five Major Categories of Loss

Health insurance addresses five broad categories of financial loss that flow from these two perils:

Medical expenses. The direct cost of diagnosis and treatment: hospital room and board, surgery, physician visits, emergency care, diagnostic imaging, and prescriptions. This is the category most people associate with health insurance — paying the actual bills generated by healthcare providers.
Disability income (loss of income from disability). When illness or injury prevents someone from working, income stops — but the mortgage, groceries, and utilities do not. Disability income coverage replaces a portion of lost earnings, typically 50–70% of pre-disability gross income, so the insured can meet everyday obligations during recovery.
Dental expenses. Routine dental care is almost universally excluded from standard major medical policies, making dental insurance a separate coverage category. It addresses preventive care (cleanings, X-rays), basic restorative work (fillings, extractions), and major procedures (crowns, bridges, dentures).
Accidental death and dismemberment (AD&D). Some accidents result not merely in injury but in death or catastrophic physical loss — the loss of a limb, hand, foot, eyesight, speech, or hearing. AD&D policies pay a lump-sum benefit, typically called the principal sum for accidental death and the capital sum (a percentage) for specific dismemberment losses. A worker who loses one hand might receive 50% of the policy's face amount.
Long-term care (LTC) / home health care. Chronic illness, cognitive impairment (such as Alzheimer's disease), or the inability to perform basic activities of daily living (ADLs) — bathing, dressing, eating, transferring — can require ongoing professional care for months or years. LTC coverage funds care in nursing homes, assisted living facilities, adult day centers, or the policyholder's own home. Without it, the cost of care can rapidly deplete retirement savings.

FAQ

Does the distinction between accident and sickness matter if my policy covers both?
Yes — even in a comprehensive policy that covers both, the distinction affects eligibility timing, benefit duration (some disability policies pay accident-related benefits longer than sickness-related benefits), and pre-existing condition analysis. Sickness can be a pre-existing condition; a sudden accident cannot.

Is a heart attack an accident or a sickness?
It is a sickness. Even though the onset is sudden, a myocardial infarction is an internal medical condition (cardiovascular disease), not an external accidental event. This matters most in accident-only policies, which would pay nothing for a heart attack.