(1) Background: The administration of subcutaneous (SC) injectables is among the most frequent procedures a nurse performs in daily practice. The needle for the injection must pass through the skin barrier to reach the SC space, where the drug will be deposited. This procedure can cause pain to the patient and local lesions. Local fat measurement can be performed by measuring the skin fold. Previous studies have found higher levels of pain in people with obesity receiving SC insulin, and this study thus aimed to measure pain levels during and after an SC injection of low-molecular-weight heparin (LMWH) and identify how age, gender, and obesity may modulate the level of pain during and after the procedure. (2) Methods: This was a cross-sectional study, and the variables included age, gender, body mass index (BMI), BMI quartile, abdominal skin folds (ASFs), ASF quartile, and pain level during and after injection. A caliper was used to measure ASFs, height and weight were used to calculate BMI, and the Visual Analog Scale (VAS) was used to measure pain. (3) Results: The sample amounted to 202 participants, which was not considered representative of the study population. The average age was 64.3 years, and females predominated (62.40%). Of these participants, 42.5% were obese, and 29.1% were overweight. The average pain levels were low during (1.4) and after injection (1.9), highlighting the absence of pain during injection in 29.7% and after injection in 34.2%. (4) Conclusions: Obesity was associated with increased pain, but when adjusted for age, the pain was no longer significant. Females and young participants showed a significant relationship with pain during injection. Age, gender, and obesity had a statistically significant relationship with pain level. Participants with obesity (according to BMI and ASF) showed the highest levels of pain during and after injection. After injection, there was an increase in pain in most cases, possibly due to the discomfort caused by the drug itself, an aspect considered in the drug’s technical data sheet as a frequent adverse effect (>1/10 to <1/100). However, the drug volume does not seem to be related to pain in this study.

Low Molecular Weight Heparin (LMWH) is commonly used as an antithrombotic in patients with reduced mobility. Its administration is performed by invasive technique (injections) that can cause pain: (1) Background: Pain and bruising are the most common side effects in patients treated with LMWH, but the skin phototype (PT) has never been included; (2) Methods: A cross-sectional descriptive study, developed in the Hospital Unit of Orthopedic and Trauma Surgery over one year. To classify all participants in the sample considering their skin PT and the different pain levels “during” and “after” the administration of enoxaparin. The STROBE checklist was used to evaluate the study. Data analyses were carried out: descriptive statistical analysis and analysis of Variance ANOVA of a non-parametric factor; (3) Results: The sample was 202 participants. The most frequent skin PTs were PT II 43.6% and PT III 33.2%. Mean pain after injection (1.96) was greater than pain during injection (1.4). Better natural protection against sunlight (high PT) would indicate greater post-injection pain; (4) Conclusions: Participants with a medium-high phototype (≥III) perceive a greater pain sensation than participants with a low phototype (≤II) after the administration of enoxaparin.