Mustard agent has extremely powerful vesicant (blistering) effects on its victims. In addition, it is strongly mutagenic and carcinogenic, due to its alkylating properties. It is also lipophilic. Because people exposed to mustard agent rarely suffer immediate symptoms, and mustard-contaminated areas may appear completely normal, victims can unknowingly receive high dosages. Within 24 hours of exposure to mustard agent, victims experience intense itching and skin irritation, which gradually turns into large blisters filled with yellow fluid wherever the mustard agent contacted the skin. These are chemical burns and are very debilitating. Mustard agent vapor easily penetrates clothing fabrics such as wool or cotton, so it is not only the exposed skin of victims that gets burned. If the victim's eyes were exposed then they become sore, starting with conjunctivitis (also known as pink eye), after which the eyelids swell, resulting in temporary blindness. In rare cases of extreme ocular exposure to mustard gas vapors, corneal ulceration, anterior chamber scarring, and neovascularization have occurred. In these severe and infrequent cases, corneal transplantation has been used as a treatment option. Miosis, when the pupil constricts more than usual, may also occur, which is probably the result of the cholinomimetic activity of mustard. At very high concentrations, if inhaled, mustard agent causes bleeding and blistering within the respiratory system, damaging mucous membranes and causing pulmonary edema. Depending on the level of contamination, mustard agent burns can vary between first and second degree burns, though they can also be every bit as severe, disfiguring and dangerous as third degree burns. Severe mustard agent burns (i.e. where more than 50% of the victim's skin has been burned) are often fatal, with death occurring after days or even weeks have passed. Mild or moderate exposure to mustard agent is unlikely to kill, though victims require lengthy periods of medical treatment and convalescence before recovery is complete.