Cryotherapy, also known as cryosurgery or cryoablation, represents a minimally invasive therapeutic approach involving the application of extremely cold liquid or instruments (cryogen) to freeze skin surface lesions. Various cryogens, such as liquid nitrogen, carbon dioxide snow, and dimethyl ether and propane (DMEP), can be employed in cryotherapy. Liquid nitrogen, with a temperature of –196°C, stands out as the most commonly utilized and effective cryogen in clinical practice.

This minimally invasive method serves as a cost-effective, simple, and relatively safe alternative to more intrusive treatments, demonstrating efficacy in an outpatient setting. Cryotherapy finds application in addressing benign skin lesions like actinic keratoses, seborrheic keratoses, viral warts, molluscum contagiosum, and skin tags. Dermatologists may also utilize cryotherapy for small skin cancers, such as superficial basal cell carcinoma (BCC) and in-situ squamous cell carcinoma (SCC) on the trunks and limbs. However, careful follow-up is imperative due to variable success rates.

Contraindications for cryotherapy include undiagnosed skin lesions, melanoma, dark-skinned patients, lesions requiring tissue pathology, those within circulation-compromised areas, patients with previous adverse reactions to cryotherapy, young children, unconscious patients, and conditions exacerbated by cold exposure (e.g., Raynaud disease, cold urticaria, cryoglobulinaemia, multiple myeloma).

The mechanism of cryotherapy involves the use of a cryogen to cool the targeted lesion to sub-zero temperatures, inducing direct tissue necrosis. The application of cryotherapy with liquid nitrogen utilizes instruments such as a cryospray, cryoprobe, or a cotton-tipped applicator. The dosage, duration of freezing, and method of delivery are contingent upon factors including the lesion’s location, depth, size, and tissue type. 

In the context of cryotherapy, various methods employing liquid nitrogen spray include the timed spot freeze technique/direct spray technique (considered the standard treatment), the paintbrush method, and the rotary or spiral spray. The timed spot freeze technique involves positioning the spray gun 1 to 1.5cm above the centre of the skin lesion and administering the spray until an ice ball encompasses the lesion and its required margin. The ice field is maintained for 5 to 30 seconds, depending on the lesion’s characteristics and freeze depth. In some cases, treatment is repeated after thawing, known as a ‘double freeze-thaw.’

Carbon dioxide cryotherapy entails creating a cylinder of frozen carbon dioxide snow or a slush combined with acetone, directly applied to the skin lesion. DMEP, available over-the-counter in aerosol form, is utilized to treat warts using a foam applicator applied to the skin lesion for 10–40 seconds, depending on its size and location.

While cryotherapy is a straightforward and relatively safe procedure, its efficacy may necessitate multiple treatments, and associated pain can impact patient compliance.

Cryosurgery can be highly effective for benign lesions like actinic and seborrheic keratoses. Actinic keratoses often require a single freeze-thaw cycle, with cure rates ranging from 39% to 83%. Seborrheic keratoses may require longer treatment times and multiple freeze-thaw cycles for thicker lesions.

In the case of viral warts, clearance rates vary based on hyperkeratosis degree and wart size. Multiple treatment sessions may be needed, with overall cure rates ranging from 39% to 84% at three months. Keratolytic pre-treatment has shown favourable response rates.

Regarding malignant lesions such as BCCs and SCCs, cryosurgery is not the primary treatment but is considered for low-risk lesions. Malignant lesions typically require multiple freeze-thaw cycles with ice field margins of 3–5mm beyond the lesion. Recurrence rates vary from 6% to 34%, necessitating regular follow-up to identify recurrence and achieve margin control.

Side effects of cryotherapy include immediate effects such as pain, paraesthesia, oedema, headache, and clear or hemorrhagic blistering. Delayed effects may include bleeding and ulceration, while other complications include secondary wound infections, nitrogen emphysema, temporary local nerve damage, permanent hypopigmentation or scarring, atrophic scarring, alopecia, and persistent or recurrent skin lesions requiring further treatment.

Post-treatment care involves providing patients with wound care instructions. Typically, no special attention is needed during the healing phase, and the treated area can be gently washed once or twice daily with soap and water. A dressing is optional but advisable for areas subject to trauma or friction. Immediate swelling and redness can be reduced with a topical steroid and oral aspirin. Blistering is common and harmless, and care should be taken to avoid picking at the scab during the healing process. Healing times vary based on the treated area.