242 Fig. 2 Ultrasound examination of the abdomen showing measure- ment of subcutaneous fat before (a) and after (b) carbon dioxide (CO2) therapy. Subepidermal thickness is reduced after carboxytherapy incidentally does not occur during carboxytherapy [7], is very well tolerated. The equipment used in this study is manufactured in Italy and approved by the European Community (EC) for medical use. Mechanism of Action Sound physiologic principles underlie the possible mech- anisms of CO2 action, modulating its effects on the skin and subdermal layers. In a histologic study, Brandi et al. [1] reported fracturing of the adipose tissue with release of triglycerides in the intercellular spaces and adipocytes presenting thin fracture lines in the plasma membrane. These lines did not involve the connective spaces where the major vascular structures are located. The dermis presented a thicker appearance than before the treatment, with the collagen ﬁbers distributed more diffusely. The same authors reported microcirculatory changes after CO2 therapy, reﬂected by increased perfusion as measured by laser Doppler ﬂowmetry and increased oxygen tension as measured by transcutaneous oxygen tension. This is to be 123 Aesth Plast Surg (2010) 34:239–243 expected from the Bohr effect on the oxygen dissociation curve. Ferreira et al. [6], in a blind, interventional, cross- sectional study, investigated CO2 injection in the dermis of Wistar rats. Treated rats showed intense collagen turnover in their skin samples compared with control animals, which had saline injections. These ﬁndings support the subjective clinical ﬁndings of improved skin texture after CO2 therapy. Cellulite Obesity is associated with decreased self-esteem and increased risk of diabetes and cardiovascular complications such as hypertension and ischemic heart disease. In a recent metaanalysis of 10 studies [8], the waist-to-height ratio, an index of abdominal obesity, was found to be a better discriminator of cardiovascular risk than body mass index (BMI). Besides liposuction, the direct therapeutic options for dealing with abdominal fat are few. Based on our results, carboxytherapy, singly or in combination, is deﬁnitely useful in this context. Subjective Beneﬁts One of the main problems of applying evidence-based medicine to aesthetics is that the beneﬁts are subjective and difﬁcult to quantify. Carboxytherapy is no exception because the main attraction of this treatment is improve- ment in skin texture and elasticity [1, 2]. Brandi et al. [4] reported improved skin elasticity after carboxytherapy, as measured by the Cutometer SEM 474 Courage-Khazaka (CK Electronics, Koln, Germany) [9–11]. This ﬁnding has been conﬁrmed by the recent development of an animal model whereby increased collagen turnover was demon- strated histologically [6]. Sex and Age Differences Our data show the beneﬁts of carboxytherapy to be limited for men. Although this can be explained by the lack of sufﬁcient male patients (n = 10), sexual dimorphism in the subdermal connective tissue is well documented [1]. This consists of a different orientation in the sexes of the sub- cutaneous ﬁbers, which extend from the dermis to the fascia, probably linked to hormonal causes [12–14]. Younger women (age, 20–29 years) appear to derive less objective beneﬁt from carboxytherapy. This supports the view that cellulite increases with age and hence the beneﬁts of carbon dioxide therapy are more quantiﬁable. Clinical Practice Consumer satisfaction is reﬂected in the widespread acceptance of carboxytherapy worldwide [2, 3]. Clearly,