The pattern of substance use has seen a shift toward opioid use being highly prevalent in Kashmir Valley with heroin being most commonly abused among them compared to cannabis, being the most common substance used in the past. Similarly, in our study the most common substance used by study cases was heroin (n = 515) followed by cannabis (n = 334). In current times, clinicians often find it difficult to detect these dangerous practices of substance use among patients, thus making it important to recognize dermatological manifestations of substance use for more effective diagnosis and practices. All the studies that we came across, during an extensive review of literature, have focused on a single substance and its cutaneous signs and never on the entire group of substances abused with respect to their dermatological manifestations. In this one-of-a-kind study, we focused on dermatological manifestations among substance users as a comprehensive cluster and attempted to study these manifestations as a group.

In the present study, pruritus was the most common dermatological symptom among substance users, which was statistically significant among heroin users (P < 0.001). Heroin and other opiates are known to induce pruritus. Many mechanisms have been put forward to explain itching post-heroin use. Opioid-induced itch has been suggested to be mediated primarily through the m-opioid receptor (MOR), a key receptor for opiates. Xian-Yu Liu et al.[11] demonstrated that this itch-specific receptor, known as MOR1D, appears to operate independently from receptors that relieve pain. Maurer et al.[12] in their study found pruritus present in 55.4% of cases in a sample size of 78, all being heroin users. They also found higher levels of histamine in cases compared to controls in the study. Elevated histamine levels due to mast cell degranulation and histamine release might have been a consequence of immune activation due to regular heroin use.[12] Our study found pruritus occurring immediately following heroin use with a duration lasting up to several days as found by Hennings et al.[2] There was a predilection of itching towards the nasal and facial areas of the cases in our study, and such findings have not been reported so far in other studies.

Staining of the fingers and nails with resulting hyperpigmentation from pale yellow to intense brown color, most commonly of the middle finger, followed by the index finger and thumb of the dominant hand, was seen in the majority of cannabis smokers (64.4%) and heroin smokers (57.1%) in our study. The mechanism of development of such lesions is similar to the development of tobacco staining of fingers where such lesions are seen due to repeated exposure to smoke and tar in smoke as mentioned by Chauhan et al.[13] Kalman et al.[14] in their study found two- to four-fold increase in the consumption of tobacco and thus staining of fingers in substance users compared to the general population.

Hyperhidrosis was seen in a few cases in the present study, specifically in opioid users, whereas it was seen in 39.6% of heroin users. Opioids are recognized as potent stimulators of mast cell degranulation, and this is thought to be the main mechanism for their diaphoretic action, resulting in excessive perspiration in heroin users. Cheshire et al.[15] found hyperhidrosis associated with opioid use in their study.

Thomson et al.[16] in their study found periodontal disease in cannabis users where they determined three cannabis exposure groups as “No exposure” (32.3%), “Some exposure” (47.4%), and “High exposure” (20.2%) and found periodontal disease in 6.5%, 11.2%, and 23.6%, respectively, concluding cannabis smoking as a risk factor for periodontal disease that is independent of the use of tobacco. Schulz-Katterbach et al.[17] found cannabis use associated with significantly higher dental decays values (P = 0.0001) than the control group in their study. Similarly, Al Bush et al.[18] in their study with a sample size of 100 found cannabis and heroin use were associated with dental decay and periodontal disease. Likewise, in the present study, tooth decay and periodontal disease were seen in 21.2% of cannabis users as well as in 19% of heroin users, concluding that both cannabis and heroin use are associated with dental decay and periodontal disease and are risk factors for these oral conditions, though the difference between the two substances was not statistically significant (P = 0.427).

Some dermatological manifestations were specific to IDUs in the present study. The presence of linear post-inflammatory hyperpigmentation at intravenous injection sites (track marks) resulting from damage and consequent sclerosis of the underlying veins and sooting tattoos formed due to injection of heroin with hot needles was seen exclusively in injectable heroin users (93.1%) in our study. Coull et al.[3] in their study with a sample size of 204 IDUs, where 60% of the cases had some skin manifestation, found a prevalence of 47% cases among them having track marks. The antecubital fossa of the non-dominant arm was the most commonly affected site in the present study similar to the description by Del Giudice.[19] Such lesions have been described in the previous literature and are known as telltale signs or stigmata of injectable drug use.

In the present study, 30.7% of injectable heroin users ended up with the presence of skin popping scars. Once the veins become sclerotic and inaccessible, drug users often resort to intradermal, subcutaneous, and sometimes intramuscular drug administration, also known as “skin popping.” This method of drug administration usually results in deep, circular, punched-out looking atrophic scars known as skin popping scars. This can be considered as another telltale sign of injectable drug use as described by Grunebaum et al.[20] Reports from European researchers show an apparent increase in skin popping among drug users.[2122]

Coull et al.[3] in their study found abscesses in the past or currently present in 75% cases followed by lumps in 48%, and leg ulcers in 25% cases. Similarly, in our study, 18.8% of injectable drug users had active skin ulcerations and skin and soft tissue infections. Several independent risk factors are present among injection drug abusers for developing SSTIs, the most important being skin popping which causes tissue trauma and introduces bacteria into the skin. It may also introduce adulterant substances, which can concentrate locally and irritate the skin.[23]

In the present study, 8.8% of injectable heroin users had the presence of puffy hands, which develops after long-term intravenous drug addiction. It was characterized by a non-pitting edema, affecting the dorsal side of fingers and hands, especially non-dominant hand with a puffy aspect similar to the description by Amode et al.[24] Female gender, injections in the hands and in the feet, and the absence of tourniquet have been found to be significant risk factors for puffy hand syndrome in the past literature.[25] In our study, male gender was predominant and the most common site was non-dominant hand followed by dominant hand, and in most of the cases history of tourniquet use while injecting heroin was lacking.

In our study, 13.7% of cannabis users had the presence of periorbital hyperpigmentation. Premature aging such as periorbital darkening, hair loss, and graying of hair has been associated with cannabis use in the literature.[26] Maharaj et al.[27] have described an increased cornification of the radial aspect of the thumb just distal to the pulp prominence on close inspection which is more easily palpated as a thickening of the corneal layer of the palmar skin of the thumb in 27 cases of heavy smoking which they have described to be due to the result of repeated friction of the thumb against the roller of cigarette lighters. Similarly, in our study, we could also find the presence of frictional callosities, especially over thumb and fingers (12.2%), developed secondary to hand rubbing of cannabis and excessive lighter use by cannabis smokers. In our study, the prevalence of acne vulgaris among substance users was 17.2%; however, the prevalence of acne vulgaris was significantly less among cannabis users (9.3%) (P < 0.001). The decreased prevalence of acne among these cases can be attributed to sebostatic effects of cannabis. Oláh et al.[28] showed that cannabidiol (CBD) derived from Cannabis sativa might improve acne vulgaris through a sebostatic mechanism. CBD had antiproliferative effects on both keratinocytes and sebocytes, thus decreasing the formation of comedones and production of sebum as well as demonstrable antimicrobial activity.[2829]

Larkin et al.[30] in a systemic review of hospital-based studies found thirteen studies reporting a positive association between hesitation cuts/repetition of self-harm and drug abuse/dependence. In the current study as well, 16.3% cases had the presence of hesitation cuts, most commonly over forearms.