- Caffeine use
- Calcium channel blocker overdose (blood pressure medication overdose)
- Calluses and corns
- Campylobacter infection (intestinal bacterial infection)
- Cancer (tumor)
- Candida albicans (yeast infection)
- Canker sores
- Carbon monoxide poisoning (odorless, poisonous gas)
- Carbuncle
- Carcinoid syndrome (flushing, diarrhea)
- Cardiac arrest (heart stops)
- Cardiac arrhythmia (abnormal heart rate)
- Cardiomegaly (enlarged heart)
- Cardiomyopathy (weakened heart)
- Carotid artery dissection (neck artery tear)
- Carotid artery stenosis (neck artery narrowing)
- Carotid cavernous fistula (abnormal blood vessel communication)
- Carpal tunnel syndrome (wrist nerve compression)
- Cat bite
- Cat scratch fever (bacterial infection after cat scratch)
- Cataracts (clouding of the eye lens)
- Cauliflower ear (wrestlers ear)
- Cavernous sinus aneurysm (head vein dilation)
- Cavernous sinus thrombosis (head vein blood clot)
- Cavernous sinus tumor (head vein cancer)
- Celiac disease (celiac sprue)
- Cellulitis (skin infection)
- Central cord syndrome (traumatic spine injury)
- Cerebellar Ataxia
- Cerebellar hemorrhage (bleeding in back of brain)
- Cerebellar syndrome (loss of coordination)
- Cerebral aneurysm (brain artery dilation)
- Cerebral contusion (bruise of brain)
- Cerebral palsy (movement disorder)
- Cerebral vascular accident (stroke)
- Cerebrospinal fluid otorrhea (leakage of brain fluid from the ear)
- Cerebrospinal fluid rhinorrhea (leakage of brain fluid from the nose)
- Cerumen impaction (ear wax buildup)
- Cervical cancer (tumor)
- Cervical dysplasia
- Cervical lymphadenopathy (enlarged neck lymph nodes)
- Cervical myelopathy (spinal cord compression)
- Cervical radiculopathy (pinched nerve in neck)
- Cervical spine fracture (broken neck bone)
- Cervical spine stenosis (narrowing of spinal canal)
- Cervical spondylosis (neck arthritis)
- Cervicitis (inflammation of the lower uterus)
- Chagas disease (trypanosomiasis)
- Chalazion
- Charcot-Marie-Tooth disease
- Cheilosis and Cheilitis
- Chemical burn
- Chest trauma (injury)
- Chicken pox (varicella virus)
- Chikungunya (viral illness from mosquitoes)
- Child abuse
- Chlamydia trachomatis infection (STD)
- Chlorine bleach ingestion
- Cholangitis (inflammation of the bile ducts)
- Cholecystitis (inflammation of the gallbladder)
- Choledocholithiasis (stone in bile duct)
- Cholelithiasis (gallstones)
- Cholera (intestinal bacterial infection)
- Cholesteatoma (middle ear mass)
- Chondromalacia (cartilage damage)
- Chronic fatigue syndrome (CFS)
- Chronic liver disease
- Chronic lymphocytic leukemia (CLL)
- Chronic myelogenous leukemia (CML)
- Chronic obstructive pulmonary disease (COPD, emphysema)
- Chronic pain
- Chronic venous insufficiency (weakened leg veins)
- Cirrhosis (liver failure and scarring)
- Clavicle fracture (broken collar bone)
- Cleft lip and palate
- Clostridium difficile (C. Diff)
- Cluster headache (one-sided headache behind the eye)
- Coarctation of aorta (narrowing of the aorta)
- Cocaine abuse
- Cocaine overdose
- Coccidiomycosis (valley fever, fungal infection)
- Cold sores and fever blisters
- Colic (prolonged infant crying episodes)
- Colitis (large intestine inflammation)
- Colon cancer (large intestine tumor)
- Colon polyps (large intestine tumors)
- Colonic diverticulitis (inflammation of pouches in the large intestine)
- Common cold (upper respiratory infection)
- Common spider bite
- Common warts
- Compartment syndrome (increased pressure inside muscles)
- Complex migraine (migraine with neurologic changes)
- Complex partial seizures (psychomotor epilepsy)
- Complex regional pain syndrome (chronic pain disorder)
- Compression fracture (broken spinal bone)
- Concussion
- Conduct disorder
- Confusion (altered mental status)
- Congenital Adrenal Hyperplasia (CAH)
- Congenital heart disease (heart defect at birth)
- Congestive heart failure (CHF)
- Conjunctivitis (pink eye)
- Constipation
- Contact dermatitis (contact skin irritation)
- Contact urticaria (hives)
- Contusion (bruise, ecchymosis)
- Conversion disorder
- Corneal abrasion (scrape on eye)
- Corneal foreign body (object in the eye)
- Corneal ulcer
- Coronary artery anomaly (heart artery malformation)
- Coronary artery disease (CAD, heart disease)
- Coronary artery dissection (heart artery tear)
- Costochondritis (chest wall inflammation)
- Cough medicine abuse
- Cradle cap (infant scalp rash)
- Crohn's disease (regional enteritis, Crohn's colitis, intestinal inflammation)
- Croup (upper airway inflammation)
- Cryptorchidism (undescended testicle)
- Cryptosporidia infection (diarrheal parasite infection)
- Cubital tunnel syndrome (nerve compression in the elbow)
- Cushing disease (excessive pituitary gland hormones)
- Cutaneous T cell lymphoma
- Cutaneous larva migrans (parasitic skin disease)
- Cyclospora infection
- Cystic fibrosis (inherited disease of lungs, digestive system)
- Cystocele (bladder hernia)
- Cytomegalovirus infection (CMV viral infection)