Thanks for your question regarding lily toxicity.  Lilies or Lilium are tall perennials ranging in height from 2 to 6 feet with numerous species. The flowers are generally large and often fragrant.  While true lily species are numerous, there are also many plants with lily in their name that are not true lilies, such as calla lily, lily of the valley among others.
Although you specifically asked about human toxicity, some lily species are highly toxic to cats, which can cause acute renal failure.  
For humans, eating certain lilies could cause a fatal reaction or death, the star lily toxicity is so well known it is known as the death camas.  Other lilies make your mouth, throat, tongue and lips go numb if eaten.  Ingestion can also cause nervous system paralysis, irregular heart rate, confusion, digestive upset, diarrhea or vomiting.  The specific lily toxin substance is not known, but the affects are well documented.  
Calcium oxalate is a serious substance, eating peace lilies and calla lilies will cause swelling of the mouth affecting the tongue, top of the mouth and lips. Skin irritation can occur in some people coming in contact with parts of certain lilies, especially the sap.  These irritating lilies include crinum lily, calla lily, true lilies, lily of the valley and belladonna lily.  
A person with plant allergies may be highly vulnerable to lily fragrance triggering issues that could complicate medical conditions under treatment.  A lovely potted lily plant in a hospital room could drip sap or drop plant parts into a patient's meal, also triggering the above symptoms. 
Available resources stated that the lily toxic substance is unnamed, but known to be liquid and ingesting this substance can be fatal.  Aldehydes are found in lily fragrances and possibly may trigger allergy reactions.  Cyanydes are present in certain seeds, such as the cherry pit or apple seed, but not in a lily plant.  Seems prudent to enjoy beautiful lilies from afar.