The burns that the patient describes are the result of too much light energy going into the skin. The way IPL works is light energy is absorbed by the pigment that we want to get rid of (in this case it is melanin in the hair) and that energy is converted to heat. The heat damages or destroys the structure holding the pigment. Not enough energy, not enough heat and nothing happens. Too much energy, too much heat and you get burned.
Some people, particularly people with darker skin, like Asians, may, as this patient did, react to with local darkening of the skin at the site of the burn. This is called post inflammatory hyperpigmentation. PIH can occur without a burn but with just too much heat.
There are several things that can be done to prevent burns and subsequent PIH. The first thing to do is make sure that the amount of energy used will do the job but not hurt the skin. The operator of the device has many ways to do this, but it requires scrupulous attention to the skin and the device as well as knowledge of the skin, the physics of photobiology and the equipment used.
The second consideration is the prevention of the resultant post inflammatory hyperpigmentation. The best way to do this is to first identify which patients are most at risk. Those with darker skin (like Asians) are at the top of the list and require special care. It may be necessary to pretreat them with a melanin inhibiting agent like hydroquinone. The IPL or laser settings must be appropriately conservative.
If a burn does occur it will most likely be a second degree burn - like a curling iron burn. It should be initially treated with a topical antibiotic ointment like Neosporin. It should heal without a scar, but there may be PIH.
If there is post inflammatory hyperpigmentation it will most likely resolve on its own after a few weeks. If it does not improve or resolve it may be treated with a melanin inhibiting agent like hydroquinone or kojic acid. I believe that IPL is contraindicated in the treatment of this temporary pigment disorder because IPL is designed to cause the heat that brought on the PIH. In the presence of the PIH there is more pigment and more light energy will be absorbed, creating more heat.
To answer the patient's direct questions: treat the burns with Neosporin, treat the PIH with hydroquinone or kojic acid when the burns have healed. Tincture of time will help, also. Unless they are third degree burns (unlikely) there will be no burn scars. Avoid future burns by avoiding further IPL or at least have a much less aggressive treatment.
This is not a simple problem. I hope this helps.