Varicella Rash and Fever Intervals
In varicella (chickenpox), new skin lesions develop in successive crops over 3-5 days, and fever typically lasts approximately 5 days, with the entire illness duration averaging 5-7 days until all lesions are crusted. 1
Timeline of Lesion Development
New lesions continue to appear for 3-5 days after the initial rash onset, creating the characteristic finding of lesions in various stages of development (macules, papules, vesicles, pustules, and crusts) present simultaneously 2, 3
The rash progresses rapidly through stages: macules quickly evolve to papules, then vesicles, pustules, and finally scabs 1
Complete crusting of all lesions typically occurs by day 5-7 after rash onset in immunocompetent individuals 1, 4, 3
Fever Duration
Fever lasts approximately 5 days in typical varicella cases 1
The duration of fever can be reduced by approximately half a day (from baseline) when oral acyclovir is initiated within 24 hours of rash onset 4, 3
Total Illness Duration
The typical duration from rash onset to complete crusting is 5-7 days in immunocompetent patients 1, 4
Treatment with oral acyclovir within 24 hours of rash onset can reduce time to 100% crusting from 7.4 days to 5.6 days 4, 3
Important Clinical Distinctions
Immunocompetent vs. Immunocompromised Patients
Immunocompromised patients may develop progressive varicella with new lesions appearing for >7 days, indicating prolonged viral replication and extended contagiousness 1, 5
Immunocompromised individuals may experience slower healing with lesions taking 7-14 days or longer to crust 5
Breakthrough Varicella (Post-Vaccination)
Breakthrough varicella in vaccinated individuals typically has a shorter duration of 4-6 days 1
The rash is more likely to be predominantly maculopapular rather than vesicular, with <50 skin lesions and low or no fever 1
Contagiousness Period
Patients are contagious from 1-2 days before rash onset until all lesions are crusted, typically 4-7 days after rash onset 1, 5
For non-crusting lesions (macules and papules), contagiousness ends when no new lesions appear within a 24-hour period 5
Common Pitfalls to Avoid
Do not assume the illness is resolving if new lesions continue to appear beyond day 5 in immunocompetent patients—this may indicate immunocompromise or complications 1, 5
Do not clear patients to return to work/school based solely on fever resolution—they remain contagious until all lesions are crusted 1, 5
In the vaccine era, do not rely solely on history of chickenpox, as only 75% of unimmunized children aged 1-4 years with a positive history are actually seropositive 1