The FDA has not approved cryotherapy as a safe and effective to treat any medical conditions.

Treating a medical condition, such as cancer, with extreme cold to freeze the abnormal cells is called cryotherapy. The United States Food and Drug Administration (FDA) has not approved cryotherapy as a safe and effective to treat any medical conditions. Side effects of cryotherapy can be categorized as immediate and subsequent side effects:

Immediate side effects include:

Pain: Pain usually begins at the time of cryotherapy and may continue even after the procedure. The patient may continue to have pain even 24 hours after the procedure. Usually, patients are given a pain reliever before and after the procedure.
Swelling with redness: The patient may initially develop some oozing, later they develop swelling and redness at the site of the procedure. These side effects may stay till 3 days. Patients may be treated with corticosteroids until contraindicated for certain conditions, such as viral warts.
Infection: Infection is usually seen with pus or oozing, which continues for a certain period. For such patients, topical antiseptic or antibiotic therapy may be initiated.
Wounds with fluid: The infection may cause skin wounds with pus or blood are called blisters. It is a very common side effect of cryotherapy. They usually heal within a few days.
Change in vitals: An increased blood pressure, reduced heart rate, and respiratory rate are usually seen if cryotherapy is used consistently or repeatedly. Patients with preexisting heart conditions and respiratory disease should be very careful before they decide about cryotherapy.
Frostbite: Mild redness to full-blown frostbite may develop after a session. Any condition that decreases sensations, such as diabetic nerve damage and heart conditions, may make an individual prone to the frostbite.
Burns: At least one user reported a frozen arm after the treatment, according to the American Academy of Dermatology. As her arm thawed, she suffered from painful swelling, blistering, and third-degree burns.
Cold panniculitis: After having eight sessions within 2 weeks, a person developed rashes that began on his lower legs and spread to his thighs, belly, and arms. It was itchy and painful. His doctor diagnosed him with cold panniculitis, which happens when the deepest layer of the skin, the fatty tissue, is injured by the cold.

Later or subsequent side effects:

Numbness: Numbness may be present if a superficial nerve is frozen. This may continue for a few months before the patient recovers from the nerve damage.
Scars: Cryotherapy may form temporary or permanent scars depending on the site of the procedure.
Skin changes: The skin exposed to cryotherapy may lighten or darken in color, especially in dark-skinned people. This may improve in months, but sometimes, it may be a permanent change.

Sometimes, other side effects like heavy bleeding are noted depending on the organ and site of the procedure.

How is cryotherapy performed?

Cryotherapy is a treatment that uses a chemical called liquid nitrogen to destroy a lesion or cancer. The liquid nitrogen is usually sprayed directly on the abnormal area until the area develops a small rim around it, which subsequently turns white (thawing). The procedure usually takes between a few seconds to minutes. Cryotherapy is usually performed for below conditions:

Cryotherapy can be used to kill off nerves that might be causing pain. A probe is inserted into the tissue next to the affected nerve. The temperature of the probe drops to effectively freeze the nerve.
It is also used to treat abnormal cells in diseases like skin cancer; the doctor usually sprays or swabs liquid nitrogen at the affected area and freezes it. The nitrogen dissolves and freezes after the procedure. A dry crust may form over the wound, which may fall along with the dead cancer cells over the next few days or after a month.
For cancers inside the body, a small probe is inserted (cryoprobe) to supply the liquid nitrogen. This can be done through the skin (percutaneously) or through a scope, depending on the position of cancer. This procedure may require general or local anesthesia. For kidney cancer, a thin, flexible tube called a laparoscope with a camera at its tip may be used to position the cryoprobe. Bronchoscopy may be needed for lung cancer and endoscopy for cancers in the food pipe to reach the tumors. Some cancers need to be frozen and thawed several times.
Cryotherapy procedure is also used to slow down the effect of severe diseases by reducing the rate of cell growth and reproduction.
Cryolipolysis is the freezing of fat cells to break them down so that they can be reabsorbed by the body. It’s a noninvasive way to remove fat cells and not damage other tissues in the body. In this procedure, the cold itself acts as an anesthetic so the patient may be awake for the entire procedure.

What is the outlook of cryotherapy?

Though it is not approved by FDA, doctors around the globe use cryotherapy as it boasts high success rates in permanently removing skin growths; even for aggressive lesions like squamous cell and basal cell cancers, studies have shown a cure rate of up to 98%. For certain types of growths, such as some forms of warts, repeat treatments over several weeks are necessary to prevent the growth's return. Successful cryotherapy avoids the need for alternative treatments, like surgery; however, the outlook remains controversial as studies are still going on about the treatment and its side effects.