Plain version: every medical expense policy has a not-covered list. Know the usual entries, and know the items California says a policy must cover anyway.
Common exclusions and limitations:
Custodial care, which falls outside the medical purpose of the policy.
Injuries covered by workers' compensation.
Experimental treatment. California adds a safeguard: for an insured with a life-threatening or seriously debilitating condition, a denial because a therapy is experimental can go to an external, independent review, and the insurer must notify eligible insureds in writing of that opportunity within five business days of the decision (Ins. Code §10145.3).
Cosmetic vs. reconstructive (Ins. Code §10123.88): a policy covering hospital, medical and surgical expenses must cover reconstructive surgery, which corrects abnormal structures caused by such things as tumors, trauma or disease, either to improve function or to create a normal appearance. Cosmetic surgery alters normal structures to improve appearance, and no coverage is required. Rebuilding a face after a tumor is removed is reconstructive; reshaping a normal nose for looks is cosmetic.
What an individual major medical policy may NOT exclude or cap:
Emergency services: an essential health benefit, so a required benefit, not a common exclusion (Ins. Code §10112.27).
Preexisting conditions: individual health benefit plans issued, amended or renewed on or after January 1, 2014, may have no preexisting condition provision, may not base eligibility on medical condition or history, and may not require a health assessment or medical questionnaire before enrollment (Ins. Code §10965.3(b), (g)).
Dollar caps: an individual health insurance policy may not set lifetime or annual limits on the dollar value of covered benefits, in or out of network (Ins. Code §10112.1). Deductibles, coinsurance and copayments are still allowed, because they share cost rather than cap what the policy pays.
One optional provision that does not reach health insurance: the Insurance Code lets a disability policy include an "intoxicants and controlled substances" provision, but that provision shall not apply to a health insurance policy (Ins. Code §10369.12(a), (b)). Many candidates assume every optional provision is available to every kind of disability policy.