Ninety percent of our scalp hair is in an active growth phase with high mitotic activity. The small blood vessels in the scalp supply the hair follicles with nutrients and carry away waste products. Any chemotherapy drugs in the bloodstream are also carried to the hair follicles, making the hair cells sensitive to the drugs.
When blood vessels in the scalp are cooled during chemotherapy, they become constricted and less of the chemotherapy drug reaches the hair follicles (Kennedy et al 1983; Parker, 1987). This vasoconstriction further leads to a reduction of the drug’s reaction rate (metabolism). Thus, the hair is less likely to fall out, decreasing the risk of alopecia. (Bülow et al, 1987; Janssen, 2007).
The effect of scalp cooling on hair cells
The degree of hair loss has appeared to be temperature-dependent. A study by Bülow et al (1985) the relationship between epicutaneous and subcutaneous temperatures of the scalp during cooling and re-warming was evaluated by using a cooling helmet in healthy subjects. Subcutaneous blood flow was reduced to about 25% during cooling. According to the results of this study, a temperature of 22°C has to be maintained for about 20 minutes in order to obtain a considerable prevention of alopecia. The authors conclude that the hair-preserving effect of scalp cooling during chemotherapy treatment is mainly due to the reduction in local tissue metabolism in response to the low temperature applied. Gregory et al (1982) have also confirmed in their study that the subcutaneous temperature of the scalp must be decreased to 22°C during the entire course of chemotherapy in order to prevent alopecia. Another researcher (Cooke et al, 1981) found that hair conservation occurs when the temperature was reduced to 24°C. Therefore, the maintenance of continual low scalp temperature is an important criteria in the treatment of hair loss during cancer therapy.
The scalp is typically cooled 15–30 minutes prior to the start of a chemotherapy treatment to reach a scalp temperature of 22°C–24°C and stay cooled for a period (post-cooling) after completed chemotherapeutic infusion. There are limited data available on the time required to cool the scalp, but a review by Grevelman and Breed (2005) described how cooling time seems to influence the success rate of the studies. In their review, the median success rate was 76% if the cooling time was 90 minutes and more, after infusion of chemotherapeutic agents. The post-cooling time is estimated as the time needed to maintain the hypothermic temperature during peak plasma drug levels, and this depends on the type of drug regimen used. Thus, drugs such as anthracyclines that have short half-life and rapid clearance from the circulation may need a short post-infusion cooling period while drugs such as cyclosphosphamide may require a longer post-infusion cooling time.