Comparison of primary and secondary syphilis and other similar skin conditions

In this frequently asked questions section, Dr. Fuzayloff answers in more detail questions about the most important points that differentiate between the two conditions.

• How can a doctor tell the  difference between herpes and syphilis?

  When a doctor examines a person with suspected herpes or syphilis, they try to put the signs and symptoms into the right context.

  
  

  What is the right context? It’s the history of the disease: what preceded the signs and symptoms, when they began appearing, how they’re evolving, and whether there are other associated symptoms.

  The time that’s passed since a risky encounter

  This is a very important point that distinguishes herpes from syphilis. Herpes blisters appear two to four days after the initial exposure. A syphilis sore, on the other hand, may take three or four weeks after exposure to appear.

  The number of sores

  Syphilis usually presents with solitary sore; very rarely, there are two to four lesions. The herpes infection presents as multiple lesions that usually are clustered and share a red base.

  The appearance of the sores

  To visually distinguish syphilis lesions from herpes lesions, follow the rule of three S’s:

  
  

  Surface

  
  

  Syphilis lesions usually have a rough, clean surface and are not filled with fluid. Herpes lesions are very superficial blister (fluid-filled sacs) or crusted sores, depending on the stage.

  
  

  Shape

  
  

  Syphilis lesions are usually round with indurated (hard) raised borders. Herpes lesions are very superficial and not felt with touch (there’s no underlying hardness of the skin).

  
  

  Size

  
  

  Syphilis lesions are up to 3 cm in diameter. Herpes lesions are only 2–3 mm in diameter.

  Associated pain

  Unlike herpes lesions, a primary syphilis sore is not painful or itchy (that’s why it goes unnoticed).

  Duration of skin symptoms

  Syphilis has a longer incubation period and it’s longer before a syphilis sore becomes visible. And it lasts longer after it appears.

  
  

  With syphilis, the lesion might take up to two weeks to become visible and up to 8 weeks to heal. It might scar after healing since the lesion penetrates the entire skin thickness.

  
  

  Herpes lesions might take one or two days to appear and on average last for two weeks (this might extend to four weeks in the first outbreak). Since the lesions are superficial, no scarring is expected after healing.

In this frequently asked questions section, Dr. Fuzayloff answers in more detail questions about the most important points that differentiate between the two conditions.

• How can secondary syphilis rash be differentiated from drug reaction rash?

  Secondary syphilis rash and drug eruption rashes can look alike and both can take different forms and shapes.

  
  

  To diagnose the rash correctly, the following are important:

  • Close examination of the rash
  • Consideration of the history of the rash
  • Testing

  Characteristics of the rash

  Appearance

  Secondary syphilis rash

  • Rough, reddish-brown, slightly raised areas on the skin. Usually, scaly on the trunk, palms, and soles.

  Allergic rash

  • Most allergic rashes (90%)—called morbilliform rash—are flat pink or red spots that may merge or become raised as the rash spreads.
  • Hives, another type of the rash that might appear, appears as raised red areas that appear and disappear within 24 hours.

  Spread and location

  Secondary syphilis rash

  • Usually affects the palms and soles first and spreads throughout the body, including the hairy part of the head
  • When it affects moist skin areas it is a raised patch called condyloma lata
  • Can form white patches inside the mouth (on the roof of the mouth)

  Allergic rash

  • Starts on the chest or back and spreads to extremities, usually symmetrically
  • Unlike secondary syphilis rash, does not affect the axilla and groin areas, hands and feet, mucous membranes (inside the mouth and vagina), or hair and nails

  Itch

  Secondary syphilis rash is usually not itchy, unlike an allergic rash, which is very itchy.

  Systemic symptoms

  Systemic symptoms are nonspecific symptoms of fever, fatigue, headache, flu-like symptoms, and enlarged lymph nodes. They indicate a more serious systemic condition. They can be present with secondary syphilis rash but not with allergic reaction.

  Duration

  • Secondary syphilis rash might take 2–6 weeks to go away, and it gets better regardless of the treatment. Treatment will speed up the process, though.
  • Unlike syphilis, an allergic rash can begin to improve within 48 hours after the causative medication is stopped. It usually resolves completely within a week. Anti-allergy medication can quickly reduce the itch and improve the appearance of the rash.

  History, or context, of the rash

  To differentiate between secondary syphilis rash and allergic rash, in addition to examination of the rash, the history, or context, of the rash is very important.

  Incubation period

  The incubation period is the time between the cause and the appearance of the rash.

  
  

  Syphilis

  
  

  For most people, the rash seems to come out of nowhere. That’s because the rash usually appears 4–8 weeks after the healing of the chancre (the primary syphilis sore). But the chancre is usually a single sore that is painless, so 60% of people miss it.

  
  

  Allergy

  
  

  A first-time allergic reaction to a medication takes longer—1–3 weeks—for the rash to develop. If it’s not the first reaction to a medication, it might take 1–3 days.

  When to suspect syphilis

  • New sexual partner
  • Multiple sexual partners
  • Homosexual male
  • Syphilis is common in your area

  When to suspect allergy

  • History of being allergic to medication
  • A new medication was used within the last two weeks
  • Eosinophilia appear on a blood test