Some chemical warfare agents, known as blister agents or vesicants, cause large, painful blisters wherever they contact skin; an example is mustard gas. Blood blister
A blood blister usually forms when a minute blood vessel close to 
the surface of the skin ruptures (breaks), and blood leaks into a tear between the layers of skin. This can happen if the skin is crushed, pinched or aggressively squeezed. Medical conditions
There are also a number of medical conditions that cause blisters. The most common are chickenpox, herpes, impetigo, and a form of eczema called dyshidrosis. Other, much rarer conditions that cause blisters include:

Bullous pemphigoid: a skin disease that causes large, tightly filled blisters to develop, usually affecting people over the age of 60. Pemphigus: a serious skin disease in which blisters develop if pressure is applied to the skin; the blisters burst easily, leaving raw areas that can become infected. Dermatitis herpetiformis: a skin disease that causes intensely itchy blisters, usually on the elbows, knees, back and buttocks. The blisters usually develop in patches of the same shape and size on both sides of the body. Chronic bullous dermatosis: a disease that causes clusters of blisters on the face, mouth or genitals. Cutaneous radiation syndrome
Epidermolysis bullosa

Pathophysiology
Friction blisters
Friction blisters are caused by excess shear stress between the bottom and surface of the skin and the body. The strata of skin around the stratum spinosum are most susceptible to shear. As the stratum spinosum tears away from the connecting tissues below, plasma from the cells diffuses out.
It is the second oral medication against COVID 19 after nirmatrelvir/ritonavir, but with a lower efficacy: about 30% (95% CI, 1–51%) against hospitalization or death in unvaccinated adults with mild or moderate COVID-19 and at least one risk factor for disease progression. Contraindications
Use during pregnancy is not recommended. There are no human data on use during pregnancy to assess the risk of adverse maternal or fetal outcomes. Based on animal data, the drug may cause fetal harm.In rats, bone and cartilage toxicity was observed after repeated dosing. Adverse effects
Adverse reactions observed in the phase III MOVe-OUT study included diarrhea (2%), nausea (1%) and dizziness (1%), all of which were mild or moderate. Overdose
The effects of overdose are unknown, treatment consists of general supportive measures such as monitoring of clinical status. Drug interactions
Based on limited available data, there are no drug interactions. Mechanism of action
Molnupiravir inhibits viral reproduction by promoting widespread mutations in the replication of viral RNA by RNA-directed RNA polymerase. It is metabolized into a ribonucleoside analog that resembles cytidine, β-D-N4-Hydroxycytidine 5′-triphosphate (also called EIDD-1931 5′-triphosphate or NHC-TP). During replication, the viruss enzyme incorporates NHC-TP into newly made RNA instead of using real cytidine. Molnupiravir can swap between two forms (tautomers), one of which mimics cytidine (C) and the other uridine (U). NHC-TP is not recognized as an error by the viruss proofreading exonuclease enzymes, which can replace mutated nucleotides with corrected versions. When the viral RNA polymerase attempts to copy RNA containing molnupiravir, it sometimes interprets it as C and sometimes as U.