Normal urine is clear or pale yellow without any strong smell. It eventually contains few air bubbles that should disappear within 10 seconds after excretion.
What is Foamy Urine?
Foamy urine has froth on top when sitting in the toilet. In truly foamy urine, bubbles will likely persist for more than 30 seconds. Foamy urine usually means the presence of proteins, which decrease the surface tension of the urine .
Except in men, who may have foamy urine due to the presence of semen (sperm) in the urine in the morning after an intercourse or wet dreams, foamy urine is not normal. Note, that normal urine will appear foamy when you urinate into a toilet that has been just cleaned using a detergent.
What Is Bubbly Urine?
In bubbly urine, gas bubbles appear in the same manner as in carbonated beverages: they arise from the fluid and disappear after they reach its surface. Bubbly urine does not look frothy. In severe case, a person can observe the passage of air out of the urethra when urinating.
Bubbles in the urine can be due to:
- The presence of gas in the urine (pneumaturia) caused by an infection with gas-producing bacteria
- The passage of air from the intestine or vagina into the bladder due to abnormal connections (fistulas) between them
Bubbly Urine Causes
A. Causes of Frothy Urine (Proteinuria)
1. Everyday situations [1,4,6]:
- Strenuous exercise
- Emotional stress
- Exposure to cold or heat
2. Orthostatic proteinuria is an increased protein excretion in the urine when a person is upright but not when he or she is lying. The urine will more likely appear frothy in the afternoon than in the morning. This harmless condition usually occurs in children and young adults .
3. Fever 
4. Heart failure, in which the increased blood flow through the kidneys results in increased protein excretion with the urine (overflow proteinuria) 
5. Kidney inflammation (glomerulonephritis, interstitial nephritis) with nephrotic syndrome, which can present with foamy urine and swelling of the face and feet 
6. Conditions with increased protein production: amyloidosis, cancers (leukemia, lymphoma, multiple myeloma), chronic inflammation (rheumatoid arthritis, sarcoidosis, Sjögren’s syndrome), infections (hepatitis, HIV/AIDS, kidney infection, malaria, syphilis), muscle breakdown (rhabdomyolysis) or sickle cell anemia [4,5,6]
7. Increased blood pressure (hypertension), especially during pregnancy (preeclampsia, eclampsia) can be associated with increased excretion of the protein called albumin in the urine (microalbuminuria) [1,2].
8. Diabetes mellitus causes foamy urine only if it is associated with a kidney damage with increased protein excretion (proteinuria or microalbuminuria) .
9. Heavy metal intoxication 
10. Chyluria refers to a milky and foamy urine caused by the chyle–a mixture of lymph, protein and fat–that leaks from the intestinal lymphatic vessels into the urine . Chyluria occurs due to an abnormal connection (fistula) between the lymphatic vessels and the urinary tract, which results in leakage of the lymph into the urine. Causes include parasitic infestations, such as filariasis, schistosomiasis and ascariasis, tuberculosis, congenital disorders of the lymphatic vessels, kidney trauma or kidney cancer [9,10].
11. Drugs: angiotensin-converting enzyme inhibitors (captopril, enalapril), antibiotics, gold, nonsteroidal anti-inflammatory drugs (aspirin, ibuprofen, indomethacin), penicillamine, phenazopyridine 
B. Causes of Bubbly Urine
1. An abnormal connection (fistula) between the intestine or vagina and bladder, for example in abscess, Crohn’s disease, ulcerative colitis, diverticulitis, colorectal cancer or after an injury or abdominal or pelvic surgery can allow the passage of air into the urine .
2. The infection of the kidneys (pyelonephritis) or bladder (cystitis) with the gas-producing bacteria (E. coli, Klebsiella, Streptococci) or the yeast Candida can be life-threatening; fever and abdominal pain are usually present .
Less Likely Causes of Foamy or Bubbly Urine
- Vaginal discharge
- An infection of the lower urinary tract (bladder and urethra)
- An infection of the prostate
- Sexually transmitted diseases, such as HIV/AIDS, gonorrhea or infection with Chlamydia
- Kidney stones
Increased bilirubin concentration in the urine due to dehydration, liver disease or hemolytic anemia can cause yellow or dark and possibly foamy urine.
Foods high in protein (meat, fish, eggs) or protein supplements (whey) by themselves do not cause foamy urine but can do so in individuals with kidney disorders.
Certain food additives (dyes) can cause colored but not likely foamy urine. Vitamin B2 (riboflavin), beta carotene and the antibiotic tetracycline can cause bright yellow urine.
Carbonated, caffeinated and alcoholic beverages do not cause foamy urine.
What To Do If You Have Foamy Or Bubbly Urine?
If you have foamy or bubbly urine and you think it is not from the semen in the urine or detergent in the toilet, visit a doctor. The first investigations you can expect are some urine and blood tests.